_.bind(func, thisArg, [partials])
97
_.bind(func, thisArg, [partials])
_.bind创建一个函数来调用func方法，会绑定this到thisArg参数上，并将partials参数插入到接收到的参数列表最前面
_.bind.placeholder值在整体构造中默认是下划线，可能在局部应用的参数中作为占位符使用
与原生的bind方法不同，本方法不设置被绑定方法的length属性（形参个数）
局部应用是指固定一个函数的一个或者多个参数
partials rest参数数组中的参数会被插入到最终参数的最前面，如果partials中有下划线代表的占位符，那么占位符处的参数会被替换成被包裹的最终方法接收的参数，按顺序从左到右替换
参数
func (Function): 需要绑定this的方法
thisArg (*): 绑定的this
[partials] (...*): 需要被局部应用的参数数组
返回值
(Function): 返回新的被绑定this的函数
例子
function greet(greeting, punctuation) { return greeting + ' ' + this.user + punctuation; } var object = { 'user': 'fred' }; var bound = _.bind(greet, object, 'hi'); bound('!'); // => 'hi fred!' // Bound with placeholders. var bound = _.bind(greet, object, _, '!'); bound('hi'); // => 'hi fred!'
源代码：
只注释了与_.bind有关的代码，其他判断情况省略
/** * lodash (Custom Build) <https://lodash.com/> * Build: `lodash modularize exports="npm" -o ./` * Copyright jQuery Foundation and other contributors <https://jquery.org/> * Released under MIT license <https://lodash.com/license> * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE> * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors */ /** Used as the `TypeError` message for "Functions" methods. */ var FUNC_ERROR_TEXT = 'Expected a function'; /** Used as the internal argument placeholder. */ var PLACEHOLDER = '__lodash_placeholder__'; /** Used to compose bitmasks for function metadata. */ var BIND_FLAG = 1, BIND_KEY_FLAG = 2, CURRY_BOUND_FLAG = 4, CURRY_FLAG = 8, CURRY_RIGHT_FLAG = 16, PARTIAL_FLAG = 32, PARTIAL_RIGHT_FLAG = 64, ARY_FLAG = 128, REARG_FLAG = 256, FLIP_FLAG = 512; /** Used as references for various `Number` constants. */ var INFINITY = 1 / 0, MAX_SAFE_INTEGER = 9007199254740991, MAX_INTEGER = 1.7976931348623157e+308, NAN = 0 / 0; /** Used to associate wrap methods with their bit flags. */ var wrapFlags = [ ['ary', ARY_FLAG], ['bind', BIND_FLAG], ['bindKey', BIND_KEY_FLAG], ['curry', CURRY_FLAG], ['curryRight', CURRY_RIGHT_FLAG], ['flip', FLIP_FLAG], ['partial', PARTIAL_FLAG], ['partialRight', PARTIAL_RIGHT_FLAG], ['rearg', REARG_FLAG] ]; /** `Object#toString` result references. */ var funcTag = '[object Function]', genTag = '[object GeneratorFunction]', symbolTag = '[object Symbol]'; /** * Used to match `RegExp` * [syntax characters](http://ecma-international.org/ecma-262/7.0/#sec-patterns). */ var reRegExpChar = /[\\^$.*+?()[\]{}|]/g; /** Used to match leading and trailing whitespace. */ var reTrim = /^\s+|\s+$/g; /** Used to match wrap detail comments. */ var reWrapComment = /\{(?:\n\/\* \[wrapped with .+\] \*\/)?\n?/, reWrapDetails = /\{\n\/\* \[wrapped with (.+)\] \*/, reSplitDetails = /,? & /; /** Used to detect bad signed hexadecimal string values. */ var reIsBadHex = /^[-+]0x[0-9a-f]+$/i; /** Used to detect binary string values. */ var reIsBinary = /^0b[01]+$/i; /** Used to detect host constructors (Safari). */ var reIsHostCtor = /^\[object .+?Constructor\]$/; /** Used to detect octal string values. */ var reIsOctal = /^0o[0-7]+$/i; /** Used to detect unsigned integer values. */ var reIsUint = /^(?:0|[1-9]\d*)$/; /** Built-in method references without a dependency on `root`. */ var freeParseInt = parseInt; /** Detect free variable `global` from Node.js. */ var freeGlobal = typeof global == 'object' && global && global.Object === Object && global; /** Detect free variable `self`. */ var freeSelf = typeof self == 'object' && self && self.Object === Object && self; /** Used as a reference to the global object. */ var root = freeGlobal || freeSelf || Function('return this')(); /** * A faster alternative to `Function#apply`, this function invokes `func` * with the `this` binding of `thisArg` and the arguments of `args`. * * @private * @param {Function} func The function to invoke. * @param {*} thisArg The `this` binding of `func`. * @param {Array} args The arguments to invoke `func` with. * @returns {*} Returns the result of `func`. */ //一个速度更快的apply方法 function apply(func, thisArg, args) { switch (args.length) { case 0: return func.call(thisArg); case 1: return func.call(thisArg, args[0]); case 2: return func.call(thisArg, args[0], args[1]); case 3: return func.call(thisArg, args[0], args[1], args[2]); } return func.apply(thisArg, args); } /** * A specialized version of `_.forEach` for arrays without support for * iteratee shorthands. * * @private * @param {Array} [array] The array to iterate over. * @param {Function} iteratee The function invoked per iteration. * @returns {Array} Returns `array`. */ //forEach方法实现 function arrayEach(array, iteratee) { var index = -1,//循环索引 length = array ? array.length : 0;//数组索引 while (++index < length) {//循环数组长度调用iteratee，如果返回值是false跳出循环 if (iteratee(array[index], index, array) === false) { break; } } return array; } /** * A specialized version of `_.includes` for arrays without support for * specifying an index to search from. * * @private * @param {Array} [array] The array to inspect. * @param {*} target The value to search for. * @returns {boolean} Returns `true` if `target` is found, else `false`. */ function arrayIncludes(array, value) { var length = array ? array.length : 0; return !!length && baseIndexOf(array, value, 0) > -1; } /** * The base implementation of `_.findIndex` and `_.findLastIndex` without * support for iteratee shorthands. * * @private * @param {Array} array The array to inspect. * @param {Function} predicate The function invoked per iteration. * @param {number} fromIndex The index to search from. * @param {boolean} [fromRight] Specify iterating from right to left. * @returns {number} Returns the index of the matched value, else `-1`. */ function baseFindIndex(array, predicate, fromIndex, fromRight) { var length = array.length, index = fromIndex + (fromRight ? 1 : -1); while ((fromRight ? index-- : ++index < length)) { if (predicate(array[index], index, array)) { return index; } } return -1; } /** * The base implementation of `_.indexOf` without `fromIndex` bounds checks. * * @private * @param {Array} array The array to inspect. * @param {*} value The value to search for. * @param {number} fromIndex The index to search from. * @returns {number} Returns the index of the matched value, else `-1`. */ function baseIndexOf(array, value, fromIndex) { if (value !== value) { return baseFindIndex(array, baseIsNaN, fromIndex); } var index = fromIndex - 1, length = array.length; while (++index < length) { if (array[index] === value) { return index; } } return -1; } /** * The base implementation of `_.isNaN` without support for number objects. * * @private * @param {*} value The value to check. * @returns {boolean} Returns `true` if `value` is `NaN`, else `false`. */ function baseIsNaN(value) { return value !== value; } /** * Gets the number of `placeholder` occurrences in `array`. * * @private * @param {Array} array The array to inspect. * @param {*} placeholder The placeholder to search for. * @returns {number} Returns the placeholder count. */ function countHolders(array, placeholder) { var length = array.length, result = 0; while (length--) { if (array[length] === placeholder) { result++; } } return result; } /** * Gets the value at `key` of `object`. * * @private * @param {Object} [object] The object to query. * @param {string} key The key of the property to get. * @returns {*} Returns the property value. */ function getValue(object, key) { return object == null ? undefined : object[key]; } /** * Checks if `value` is a host object in IE < 9. * * @private * @param {*} value The value to check. * @returns {boolean} Returns `true` if `value` is a host object, else `false`. */ function isHostObject(value) { // Many host objects are `Object` objects that can coerce to strings // despite having improperly defined `toString` methods. var result = false; if (value != null && typeof value.toString != 'function') { try { result = !!(value + ''); } catch (e) {} } return result; } /** * Replaces all `placeholder` elements in `array` with an internal placeholder * and returns an array of their indexes. * * @private * @param {Array} array The array to modify. * @param {*} placeholder The placeholder to replace. * @returns {Array} Returns the new array of placeholder indexes. */ //替换数组中所有占位符元素为内部占位符然后返回一个它们的索引的数组 function replaceHolders(array, placeholder) { var index = -1,//循环索引 length = array.length,//数组长度 resIndex = 0, result = [];//结果数组 while (++index < length) { var value = array[index];//数组的当前值 if (value === placeholder || value === PLACEHOLDER) {//如果当前值是占位符 array[index] = PLACEHOLDER;//就替换成内部占位符 result[resIndex++] = index;//结果数组是数组中占位符的索引 } } return result; } /** Used for built-in method references. */ var funcProto = Function.prototype, objectProto = Object.prototype; /** Used to detect overreaching core-js shims. */ var coreJsData = root['__core-js_shared__']; /** Used to detect methods masquerading as native. */ var maskSrcKey = (function() { var uid = /[^.]+$/.exec(coreJsData && coreJsData.keys && coreJsData.keys.IE_PROTO || ''); return uid ? ('Symbol(src)_1.' + uid) : ''; }()); /** Used to resolve the decompiled source of functions. */ var funcToString = funcProto.toString; /** Used to check objects for own properties. */ var hasOwnProperty = objectProto.hasOwnProperty; /** * Used to resolve the * [`toStringTag`](http://ecma-international.org/ecma-262/7.0/#sec-object.prototype.tostring) * of values. */ var objectToString = objectProto.toString; /** Used to detect if a method is native. */ var reIsNative = RegExp('^' + funcToString.call(hasOwnProperty).replace(reRegExpChar, '\\$&') .replace(/hasOwnProperty|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$' ); /** Built-in value references. */ var objectCreate = Object.create; /* Built-in method references for those with the same name as other `lodash` methods. */ var nativeMax = Math.max, nativeMin = Math.min; /* Used to set `toString` methods. */ var defineProperty = (function() { var func = getNative(Object, 'defineProperty'), name = getNative.name; return (name && name.length > 2) ? func : undefined; }()); /** * The base implementation of `_.create` without support for assigning * properties to the created object. * * @private * @param {Object} prototype The object to inherit from. * @returns {Object} Returns the new object. */ function baseCreate(proto) { return isObject(proto) ? objectCreate(proto) : {}; } /** * The base implementation of `_.isNative` without bad shim checks. * * @private * @param {*} value The value to check. * @returns {boolean} Returns `true` if `value` is a native function, * else `false`. */ function baseIsNative(value) { if (!isObject(value) || isMasked(value)) { return false; } var pattern = (isFunction(value) || isHostObject(value)) ? reIsNative : reIsHostCtor; return pattern.test(toSource(value)); } /** * The base implementation of `_.rest` which doesn't validate or coerce arguments. * * @private * @param {Function} func The function to apply a rest parameter to. * @param {number} [start=func.length-1] The start position of the rest parameter. * @returns {Function} Returns the new function. */ //_.rest方法的基础实现，为函数实现ES6的rest参数 //rest参数的起始位置，默认是形参个数减去1，func.length - 1 function baseRest(func, start) { start = nativeMax(start === undefined ? (func.length - 1) : start, 0); //处理rest参数的起始位置,如果没传递start，就用函数形参个数减一，如果传递了，就在start和0之间选一个最大值 return function() { var args = arguments,//函数接收到的参数数组 index = -1,//循环索引 length = nativeMax(args.length - start, 0),//rest参数的长度 array = Array(length);//创建一个长度为rest参数长度的数组 while (++index < length) {//循环rest参数长度，将rest参数全部存入array变量中 array[index] = args[start + index]; } index = -1;//循环参数 var otherArgs = Array(start + 1);//创建一个数组存放除了rest参数以外的其他参数 while (++index < start) {//循环获取其他参数存入otherArgs中 otherArgs[index] = args[index]; } otherArgs[start] = array;//otherArgs的最后一个参数就是rest参数数组 return apply(func, this, otherArgs);//调用func，参数已处理成带有rest参数的形式 }; } /** * Creates an array that is the composition of partially applied arguments, * placeholders, and provided arguments into a single array of arguments. * * @private * @param {Array} args The provided arguments. * @param {Array} partials The arguments to prepend to those provided. * @param {Array} holders The `partials` placeholder indexes. * @params {boolean} [isCurried] Specify composing for a curried function. * @returns {Array} Returns the new array of composed arguments. */ //将局部应用参数，占位符和其他被提供的参数处理成最终结果参数数组返回 function composeArgs(args, partials, holders, isCurried) { var argsIndex = -1,//包裹方法接收到的参数数组循环索引 argsLength = args.length,//包裹方法接收到的参数长度 holdersLength = holders.length,//占位符索引数组的长度 leftIndex = -1,//partials循环索引 leftLength = partials.length,//partials长度 rangeLength = nativeMax(argsLength - holdersLength, 0), //包裹方法接收到的参数长度减去占位符长度，需要填充占位符的包裹方法接收到的参数去除后剩余的参数长度 result = Array(leftLength + rangeLength),//结果数组初始化 isUncurried = !isCurried; while (++leftIndex < leftLength) {//先将局部应用参数插入结果数组 result[leftIndex] = partials[leftIndex]; } while (++argsIndex < holdersLength) { if (isUncurried || argsIndex < argsLength) { result[holders[argsIndex]] = args[argsIndex]; //将占位符处的参数替换成包裹方法接收到的参数的开头对应的参数 } } while (rangeLength--) { //需要填充占位符的包裹方法接收到的参数去除后剩余的参数插入结果数组最后 result[leftIndex++] = args[argsIndex++]; } return result; } /** * This function is like `composeArgs` except that the arguments composition * is tailored for `_.partialRight`. * * @private * @param {Array} args The provided arguments. * @param {Array} partials The arguments to append to those provided. * @param {Array} holders The `partials` placeholder indexes. * @params {boolean} [isCurried] Specify composing for a curried function. * @returns {Array} Returns the new array of composed arguments. */ function composeArgsRight(args, partials, holders, isCurried) { var argsIndex = -1, argsLength = args.length, holdersIndex = -1, holdersLength = holders.length, rightIndex = -1, rightLength = partials.length, rangeLength = nativeMax(argsLength - holdersLength, 0), result = Array(rangeLength + rightLength), isUncurried = !isCurried; while (++argsIndex < rangeLength) { result[argsIndex] = args[argsIndex]; } var offset = argsIndex; while (++rightIndex < rightLength) { result[offset + rightIndex] = partials[rightIndex]; } while (++holdersIndex < holdersLength) { if (isUncurried || argsIndex < argsLength) { result[offset + holders[holdersIndex]] = args[argsIndex++]; } } return result; } /** * Copies the values of `source` to `array`. * * @private * @param {Array} source The array to copy values from. * @param {Array} [array=[]] The array to copy values to. * @returns {Array} Returns `array`. */ function copyArray(source, array) { var index = -1, length = source.length; array || (array = Array(length)); while (++index < length) { array[index] = source[index]; } return array; } /** * Creates a function that wraps `func` to invoke it with the optional `this` * binding of `thisArg`. * * @private * @param {Function} func The function to wrap. * @param {number} bitmask The bitmask flags. See `createWrap` for more details. * @param {*} [thisArg] The `this` binding of `func`. * @returns {Function} Returns the new wrapped function. */ //创建一个函数包裹func，会在调用func的时候将this绑定到可选的thisArg参数上 function createBind(func, bitmask, thisArg) { var isBind = bitmask & BIND_FLAG,//判断是否是处理_.bind调用 Ctor = createCtor(func);//创建只能够构造调用版本的func，也就是只能new调用 function wrapper() {//创建包裹函数 var fn = (this && this !== root && this instanceof wrapper) ? Ctor : func; //如果this对象不是顶层全局对象并且继承自wrapper，就将fn变成无论如何调用都是new调用的构造函数 //否则还使用func return fn.apply(isBind ? thisArg : this, arguments); //将fn在thisArg上绑定调用 } return wrapper; } /** * Creates a function that produces an instance of `Ctor` regardless of * whether it was invoked as part of a `new` expression or by `call` or `apply`. * * @private * @param {Function} Ctor The constructor to wrap. * @returns {Function} Returns the new wrapped function. */ //创建一个函数，它能够生成Ctor的新实例不管它是否被new调用或者call和apply调用 function createCtor(Ctor) { return function() { // Use a `switch` statement to work with class constructors. See // http://ecma-international.org/ecma-262/7.0/#sec-ecmascript-function-objects-call-thisargument-argumentslist // for more details. var args = arguments; switch (args.length) {//0~7的参数的时候直接返回new Ctor case 0: return new Ctor; case 1: return new Ctor(args[0]); case 2: return new Ctor(args[0], args[1]); case 3: return new Ctor(args[0], args[1], args[2]); case 4: return new Ctor(args[0], args[1], args[2], args[3]); case 5: return new Ctor(args[0], args[1], args[2], args[3], args[4]); case 6: return new Ctor(args[0], args[1], args[2], args[3], args[4], args[5]); case 7: return new Ctor(args[0], args[1], args[2], args[3], args[4], args[5], args[6]); } var thisBinding = baseCreate(Ctor.prototype),//this对象，是继承自Ctor.prototype的新对象 result = Ctor.apply(thisBinding, args);//apply调用Ctor // Mimic the constructor's `return` behavior. // See https://es5.github.io/#x13.2.2 for more details. //模仿构造函数的return行为 return isObject(result) ? result : thisBinding; }; } /** * Creates a function that wraps `func` to enable currying. * * @private * @param {Function} func The function to wrap. * @param {number} bitmask The bitmask flags. See `createWrap` for more details. * @param {number} arity The arity of `func`. * @returns {Function} Returns the new wrapped function. */ function createCurry(func, bitmask, arity) { var Ctor = createCtor(func); function wrapper() { var length = arguments.length, args = Array(length), index = length, placeholder = getHolder(wrapper); while (index--) { args[index] = arguments[index]; } var holders = (length < 3 && args[0] !== placeholder && args[length - 1] !== placeholder) ? [] : replaceHolders(args, placeholder); length -= holders.length; if (length < arity) { return createRecurry( func, bitmask, createHybrid, wrapper.placeholder, undefined, args, holders, undefined, undefined, arity - length); } var fn = (this && this !== root && this instanceof wrapper) ? Ctor : func; return apply(fn, this, args); } return wrapper; } /** * Creates a function that wraps `func` to invoke it with optional `this` * binding of `thisArg`, partial application, and currying. * * @private * @param {Function|string} func The function or method name to wrap. * @param {number} bitmask The bitmask flags. See `createWrap` for more details. * @param {*} [thisArg] The `this` binding of `func`. * @param {Array} [partials] The arguments to prepend to those provided to * the new function. * @param {Array} [holders] The `partials` placeholder indexes. * @param {Array} [partialsRight] The arguments to append to those provided * to the new function. * @param {Array} [holdersRight] The `partialsRight` placeholder indexes. * @param {Array} [argPos] The argument positions of the new function. * @param {number} [ary] The arity cap of `func`. * @param {number} [arity] The arity of `func`. * @returns {Function} Returns the new wrapped function. */ //创建一个方法将func方法包裹，实现this绑定，或者部分应用或者柯里化 function createHybrid(func, bitmask, thisArg, partials, holders, partialsRight, holdersRight, argPos, ary, arity) { var isAry = bitmask & ARY_FLAG, isBind = bitmask & BIND_FLAG,//对应_.bind isBindKey = bitmask & BIND_KEY_FLAG, isCurried = bitmask & (CURRY_FLAG | CURRY_RIGHT_FLAG), isFlip = bitmask & FLIP_FLAG, Ctor = isBindKey ? undefined : createCtor(func); function wrapper() { var length = arguments.length,//包裹函数接收到的参数长度 args = Array(length),//处理好的结果参数列表初始化 index = length; while (index--) {//将接收到的参数赋值到结果参数数组里 args[index] = arguments[index]; } if (isCurried) { var placeholder = getHolder(wrapper), holdersCount = countHolders(args, placeholder); } if (partials) {//如果传递了partials局部应用参数数组，调用composeArgs处理参数 args = composeArgs(args, partials, holders, isCurried); } if (partialsRight) { args = composeArgsRight(args, partialsRight, holdersRight, isCurried); } length -= holdersCount; if (isCurried && length < arity) { var newHolders = replaceHolders(args, placeholder); return createRecurry( func, bitmask, createHybrid, wrapper.placeholder, thisArg, args, newHolders, argPos, ary, arity - length ); } var thisBinding = isBind ? thisArg : this, fn = isBindKey ? thisBinding[func] : func; length = args.length; if (argPos) { args = reorder(args, argPos); } else if (isFlip && length > 1) { args.reverse(); } if (isAry && ary < length) { args.length = ary; } if (this && this !== root && this instanceof wrapper) { fn = Ctor || createCtor(fn); } return fn.apply(thisBinding, args); } return wrapper; } /** * Creates a function that wraps `func` to invoke it with the `this` binding * of `thisArg` and `partials` prepended to the arguments it receives. * * @private * @param {Function} func The function to wrap. * @param {number} bitmask The bitmask flags. See `createWrap` for more details. * @param {*} thisArg The `this` binding of `func`. * @param {Array} partials The arguments to prepend to those provided to * the new function. * @returns {Function} Returns the new wrapped function. */ //既绑定this也处理局部应用参数 function createPartial(func, bitmask, thisArg, partials) { var isBind = bitmask & BIND_FLAG,//判断掩码二进制位上是否有_.bind操作对应的位 Ctor = createCtor(func);//创建只能够构造调用版本的func，也就是只能new调用 function wrapper() { var argsIndex = -1,//参数列表循环索引 argsLength = arguments.length,//包裹后的方法接收的参数列表 leftIndex = -1,//左循环索引 leftLength = partials.length,//需要局部应用处理的参数数组 args = Array(leftLength + argsLength),//最终处理好的结果参数数组初始化 fn = (this && this !== root && this instanceof wrapper) ? Ctor : func; while (++leftIndex < leftLength) {//循环partials，将partials中参数插入到参数列表开头 args[leftIndex] = partials[leftIndex]; } while (argsLength--) {//将包裹后函数接收的参数连接到参数列表后面 args[leftIndex++] = arguments[++argsIndex]; } return apply(fn, isBind ? thisArg : this, args); } return wrapper; } /** * Creates a function that wraps `func` to continue currying. * * @private * @param {Function} func The function to wrap. * @param {number} bitmask The bitmask flags. See `createWrap` for more details. * @param {Function} wrapFunc The function to create the `func` wrapper. * @param {*} placeholder The placeholder value. * @param {*} [thisArg] The `this` binding of `func`. * @param {Array} [partials] The arguments to prepend to those provided to * the new function. * @param {Array} [holders] The `partials` placeholder indexes. * @param {Array} [argPos] The argument positions of the new function. * @param {number} [ary] The arity cap of `func`. * @param {number} [arity] The arity of `func`. * @returns {Function} Returns the new wrapped function. */ function createRecurry(func, bitmask, wrapFunc, placeholder, thisArg, partials, holders, argPos, ary, arity) { var isCurry = bitmask & CURRY_FLAG, newHolders = isCurry ? holders : undefined, newHoldersRight = isCurry ? undefined : holders, newPartials = isCurry ? partials : undefined, newPartialsRight = isCurry ? undefined : partials; bitmask |= (isCurry ? PARTIAL_FLAG : PARTIAL_RIGHT_FLAG); bitmask &= ~(isCurry ? PARTIAL_RIGHT_FLAG : PARTIAL_FLAG); if (!(bitmask & CURRY_BOUND_FLAG)) { bitmask &= ~(BIND_FLAG | BIND_KEY_FLAG); } var result = wrapFunc(func, bitmask, thisArg, newPartials, newHolders, newPartialsRight, newHoldersRight, argPos, ary, arity); result.placeholder = placeholder; return setWrapToString(result, func, bitmask); } /** * Creates a function that either curries or invokes `func` with optional * `this` binding and partially applied arguments. * * @private * @param {Function|string} func The function or method name to wrap. * @param {number} bitmask The bitmask flags. * The bitmask may be composed of the following flags: * 1 - `_.bind` * 2 - `_.bindKey` * 4 - `_.curry` or `_.curryRight` of a bound function * 8 - `_.curry` * 16 - `_.curryRight` * 32 - `_.partial` * 64 - `_.partialRight` * 128 - `_.rearg` * 256 - `_.ary` * 512 - `_.flip` * @param {*} [thisArg] The `this` binding of `func`. * @param {Array} [partials] The arguments to be partially applied. * @param {Array} [holders] The `partials` placeholder indexes. * @param {Array} [argPos] The argument positions of the new function. * @param {number} [ary] The arity cap of `func`. * @param {number} [arity] The arity of `func`. * @returns {Function} Returns the new wrapped function. */ //创建包裹好的函数，做柯里化或者绑定this或者处理局部应用参数 function createWrap(func, bitmask, thisArg, partials, holders, argPos, ary, arity) { var isBindKey = bitmask & BIND_KEY_FLAG; if (!isBindKey && typeof func != 'function') { //如果不是_.bindKey调用就判断func是否是函数类型，不是就抛出错误 throw new TypeError(FUNC_ERROR_TEXT); } var length = partials ? partials.length : 0;//局部应用参数数组的长度 if (!length) {//如果partials长度为0 bitmask &= ~(PARTIAL_FLAG | PARTIAL_RIGHT_FLAG); //bitmask等于自身和PARTIAL_FLAG和PARTIAL_RIGHT_FLAG对应二进制位上没有置位进行按位与运算的结果 partials = holders = undefined; //partials局部应用参数数组和holders占位符对应索引数组都赋为undefined } ary = ary === undefined ? ary : nativeMax(toInteger(ary), 0); arity = arity === undefined ? arity : toInteger(arity); length -= holders ? holders.length : 0; //局部应用参数数组的长度减掉占位符的长度 if (bitmask & PARTIAL_RIGHT_FLAG) {//对应_.partialRight方法 //处理partialRight，holdersRight和partials和holders变量 var partialsRight = partials, holdersRight = holders; partials = holders = undefined; } var newData = [ func, bitmask, thisArg, partials, holders, partialsRight, holdersRight, argPos, ary, arity ];//处理好的参数数组 func = newData[0]; bitmask = newData[1]; thisArg = newData[2]; partials = newData[3]; holders = newData[4]; arity = newData[9] = newData[9] == null ? (isBindKey ? 0 : func.length) : nativeMax(newData[9] - length, 0); if (!arity && bitmask & (CURRY_FLAG | CURRY_RIGHT_FLAG)) { bitmask &= ~(CURRY_FLAG | CURRY_RIGHT_FLAG); } if (!bitmask || bitmask == BIND_FLAG) { //对应调用_.bind方法，单纯绑定this的处理 var result = createBind(func, bitmask, thisArg); } else if (bitmask == CURRY_FLAG || bitmask == CURRY_RIGHT_FLAG) { result = createCurry(func, bitmask, arity); } else if ((bitmask == PARTIAL_FLAG || bitmask == (BIND_FLAG | PARTIAL_FLAG)) && !holders.length) { //BIND_FLAG | PARTIAL_FLAG的时候处理，即绑定this也处理局部应用参数 //此处只适用于局部应用参数中没有占位符的情况 result = createPartial(func, bitmask, thisArg, partials); } else { //BIND_FLAG | PARTIAL_FLAG有占位符的时候就得执行这里 result = createHybrid.apply(undefined, newData); } return setWrapToString(result, func, bitmask); } /** * Gets the argument placeholder value for `func`. * * @private * @param {Function} func The function to inspect. * @returns {*} Returns the placeholder value. */ //获取对于func的参数占位符的值 function getHolder(func) { var object = func; return object.placeholder; } /** * Gets the native function at `key` of `object`. * * @private * @param {Object} object The object to query. * @param {string} key The key of the method to get. * @returns {*} Returns the function if it's native, else `undefined`. */ function getNative(object, key) { var value = getValue(object, key); return baseIsNative(value) ? value : undefined; } /** * Extracts wrapper details from the `source` body comment. * * @private * @param {string} source The source to inspect. * @returns {Array} Returns the wrapper details. */ //提取包裹函数细节 function getWrapDetails(source) { var match = source.match(reWrapDetails); return match ? match[1].split(reSplitDetails) : []; } /** * Inserts wrapper `details` in a comment at the top of the `source` body. * * @private * @param {string} source The source to modify. * @returns {Array} details The details to insert. * @returns {string} Returns the modified source. */ //包裹的方法调用了什么操作，生成对应字符串说明 function insertWrapDetails(source, details) { var length = details.length, lastIndex = length - 1; details[lastIndex] = (length > 1 ? '& ' : '') + details[lastIndex]; details = details.join(length > 2 ? ', ' : ' '); return source.replace(reWrapComment, '{\n/* [wrapped with ' + details + '] */\n'); } /** * Checks if `value` is a valid array-like index. * * @private * @param {*} value The value to check. * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index. * @returns {boolean} Returns `true` if `value` is a valid index, else `false`. */ function isIndex(value, length) { length = length == null ? MAX_SAFE_INTEGER : length; return !!length && (typeof value == 'number' || reIsUint.test(value)) && (value > -1 && value % 1 == 0 && value < length); } /** * Checks if `func` has its source masked. * * @private * @param {Function} func The function to check. * @returns {boolean} Returns `true` if `func` is masked, else `false`. */ function isMasked(func) { return !!maskSrcKey && (maskSrcKey in func); } /** * Reorder `array` according to the specified indexes where the element at * the first index is assigned as the first element, the element at * the second index is assigned as the second element, and so on. * * @private * @param {Array} array The array to reorder. * @param {Array} indexes The arranged array indexes. * @returns {Array} Returns `array`. */ function reorder(array, indexes) { var arrLength = array.length, length = nativeMin(indexes.length, arrLength), oldArray = copyArray(array); while (length--) { var index = indexes[length]; array[length] = isIndex(index, arrLength) ? oldArray[index] : undefined; } return array; } /** * Sets the `toString` method of `wrapper` to mimic the source of `reference` * with wrapper details in a comment at the top of the source body. * * @private * @param {Function} wrapper The function to modify. * @param {Function} reference The reference function. * @param {number} bitmask The bitmask flags. See `createWrap` for more details. * @returns {Function} Returns `wrapper`. */ //为wrapper设置toString方法模拟源引用，toString将返回wrapper细节的评论字符串 var setWrapToString = !defineProperty ? identity : function(wrapper, reference, bitmask) { var source = (reference + ''); return defineProperty(wrapper, 'toString', { 'configurable': true, 'enumerable': false, 'value': constant(insertWrapDetails(source, updateWrapDetails(getWrapDetails(source), bitmask))) }); }; /** * Converts `func` to its source code. * * @private * @param {Function} func The function to process. * @returns {string} Returns the source code. */ function toSource(func) { if (func != null) { try { return funcToString.call(func); } catch (e) {} try { return (func + ''); } catch (e) {} } return ''; } /** * Updates wrapper `details` based on `bitmask` flags. * * @private * @returns {Array} details The details to modify. * @param {number} bitmask The bitmask flags. See `createWrap` for more details. * @returns {Array} Returns `details`. */ //更新包裹函数细节，添加掩码对应的调用函数信息 function updateWrapDetails(details, bitmask) { arrayEach(wrapFlags, function(pair) {//循环包裹处理的原方法和对应掩码的数组 var value = '_.' + pair[0];//方法名 if ((bitmask & pair[1]) && !arrayIncludes(details, value)) { //如果掩码对应并且details包含函数名，例如_.bind，就将当前函数名插入details最后面 details.push(value); } }); return details.sort();//返回排序后的details } /** * Creates a function that invokes `func` with the `this` binding of `thisArg` * and `partials` prepended to the arguments it receives. * * The `_.bind.placeholder` value, which defaults to `_` in monolithic builds, * may be used as a placeholder for partially applied arguments. * * **Note:** Unlike native `Function#bind`, this method doesn't set the "length" * property of bound functions. * * @static * @memberOf _ * @since 0.1.0 * @category Function * @param {Function} func The function to bind. * @param {*} thisArg The `this` binding of `func`. * @param {...*} [partials] The arguments to be partially applied. * @returns {Function} Returns the new bound function. * @example * * function greet(greeting, punctuation) { * return greeting + ' ' + this.user + punctuation; * } * * var object = { 'user': 'fred' }; * * var bound = _.bind(greet, object, 'hi'); * bound('!'); * // => 'hi fred!' * * // Bound with placeholders. * var bound = _.bind(greet, object, _, '!'); * bound('hi'); * // => 'hi fred!' */ //创建一个函数来调用func方法，会绑定this到thisArg参数上，并将partials参数插入到接收到的参数列表最前面 //_.bind.placeholder值在整体构造中默认是下划线，可能在局部应用的参数中作为占位符使用 //与原生的bind方法不同，本方法不设置被绑定方法的length属性（形参个数） //局部应用是指固定一个函数的一个或者多个参数 //partials rest参数数组中的参数会被插入到最终参数的最前面，如果partials中有下划线代表的占位符，那么占位符处的参数会被替换成被包裹的最终方法接收的参数，按顺序从左到右替换 var bind = baseRest(function(func, thisArg, partials) { var bitmask = BIND_FLAG;//_.bind调用对应的掩码 if (partials.length) {//如果partials参数拥有length属性 var holders = replaceHolders(partials, getHolder(bind)); //将partials数组中的占位符替换成内部占位符，然后返回partials数组中占位符位置的索引组成的数组 bitmask |= PARTIAL_FLAG;//掩码也添加上局部应用的对应位，也就是BIND_FLAG \ PARTIAL_FLAG } return createWrap(func, bitmask, thisArg, partials, holders); //调用createWrap包裹func }); /** * Checks if `value` is classified as a `Function` object. * * @static * @memberOf _ * @since 0.1.0 * @category Lang * @param {*} value The value to check. * @returns {boolean} Returns `true` if `value` is a function, else `false`. * @example * * _.isFunction(_); * // => true * * _.isFunction(/abc/); * // => false */ function isFunction(value) { // The use of `Object#toString` avoids issues with the `typeof` operator // in Safari 8-9 which returns 'object' for typed array and other constructors. var tag = isObject(value) ? objectToString.call(value) : ''; return tag == funcTag || tag == genTag; } /** * Checks if `value` is the * [language type](http://www.ecma-international.org/ecma-262/7.0/#sec-ecmascript-language-types) * of `Object`. (e.g. arrays, functions, objects, regexes, `new Number(0)`, and `new String('')`) * * @static * @memberOf _ * @since 0.1.0 * @category Lang * @param {*} value The value to check. * @returns {boolean} Returns `true` if `value` is an object, else `false`. * @example * * _.isObject({}); * // => true * * _.isObject([1, 2, 3]); * // => true * * _.isObject(_.noop); * // => true * * _.isObject(null); * // => false */ function isObject(value) { var type = typeof value; return !!value && (type == 'object' || type == 'function'); } /** * Checks if `value` is object-like. A value is object-like if it's not `null` * and has a `typeof` result of "object". * * @static * @memberOf _ * @since 4.0.0 * @category Lang * @param {*} value The value to check. * @returns {boolean} Returns `true` if `value` is object-like, else `false`. * @example * * _.isObjectLike({}); * // => true * * _.isObjectLike([1, 2, 3]); * // => true * * _.isObjectLike(_.noop); * // => false * * _.isObjectLike(null); * // => false */ function isObjectLike(value) { return !!value && typeof value == 'object'; } /** * Checks if `value` is classified as a `Symbol` primitive or object. * * @static * @memberOf _ * @since 4.0.0 * @category Lang * @param {*} value The value to check. * @returns {boolean} Returns `true` if `value` is a symbol, else `false`. * @example * * _.isSymbol(Symbol.iterator); * // => true * * _.isSymbol('abc'); * // => false */ function isSymbol(value) { return typeof value == 'symbol' || (isObjectLike(value) && objectToString.call(value) == symbolTag); } /** * Converts `value` to a finite number. * * @static * @memberOf _ * @since 4.12.0 * @category Lang * @param {*} value The value to convert. * @returns {number} Returns the converted number. * @example * * _.toFinite(3.2); * // => 3.2 * * _.toFinite(Number.MIN_VALUE); * // => 5e-324 * * _.toFinite(Infinity); * // => 1.7976931348623157e+308 * * _.toFinite('3.2'); * // => 3.2 */ function toFinite(value) { if (!value) { return value === 0 ? value : 0; } value = toNumber(value); if (value === INFINITY || value === -INFINITY) { var sign = (value < 0 ? -1 : 1); return sign * MAX_INTEGER; } return value === value ? value : 0; } /** * Converts `value` to an integer. * * **Note:** This method is loosely based on * [`ToInteger`](http://www.ecma-international.org/ecma-262/7.0/#sec-tointeger). * * @static * @memberOf _ * @since 4.0.0 * @category Lang * @param {*} value The value to convert. * @returns {number} Returns the converted integer. * @example * * _.toInteger(3.2); * // => 3 * * _.toInteger(Number.MIN_VALUE); * // => 0 * * _.toInteger(Infinity); * // => 1.7976931348623157e+308 * * _.toInteger('3.2'); * // => 3 */ function toInteger(value) { var result = toFinite(value), remainder = result % 1; return result === result ? (remainder ? result - remainder : result) : 0; } /** * Converts `value` to a number. * * @static * @memberOf _ * @since 4.0.0 * @category Lang * @param {*} value The value to process. * @returns {number} Returns the number. * @example * * _.toNumber(3.2); * // => 3.2 * * _.toNumber(Number.MIN_VALUE); * // => 5e-324 * * _.toNumber(Infinity); * // => Infinity * * _.toNumber('3.2'); * // => 3.2 */ function toNumber(value) { if (typeof value == 'number') { return value; } if (isSymbol(value)) { return NAN; } if (isObject(value)) { var other = typeof value.valueOf == 'function' ? value.valueOf() : value; value = isObject(other) ? (other + '') : other; } if (typeof value != 'string') { return value === 0 ? value : +value; } value = value.replace(reTrim, ''); var isBinary = reIsBinary.test(value); return (isBinary || reIsOctal.test(value)) ? freeParseInt(value.slice(2), isBinary ? 2 : 8) : (reIsBadHex.test(value) ? NAN : +value); } /** * Creates a function that returns `value`. * * @static * @memberOf _ * @since 2.4.0 * @category Util * @param {*} value The value to return from the new function. * @returns {Function} Returns the new constant function. * @example * * var objects = _.times(2, _.constant({ 'a': 1 })); * * console.log(objects); * // => [{ 'a': 1 }, { 'a': 1 }] * * console.log(objects[0] === objects[1]); * // => true */ //创建一个方法永远返回指定值 function constant(value) { return function() { return value; }; } /** * This method returns the first argument it receives. * * @static * @since 0.1.0 * @memberOf _ * @category Util * @param {*} value Any value. * @returns {*} Returns `value`. * @example * * var object = { 'a': 1 }; * * console.log(_.identity(object) === object); * // => true */ function identity(value) { return value; } // Assign default placeholders. bind.placeholder = {}; module.exports = bind;
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