_.isNaN(value)

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_.isNaN(value)

_.isNaN检查一个值是否是NaN

此方法基于Number.isNaN，和全局的isNaN不一样

参数

value (*): 需要检查的值

返回值

(boolean): 如果是NaN返回true，否则false

例子

_.isNaN(NaN);
// => true
 
_.isNaN(new Number(NaN));
// => true
 
isNaN(undefined);
// => true
 
_.isNaN(undefined);
// => false

源代码

/**
 * lodash (Custom Build) <https://lodash.com/>
 * Build: `lodash modularize exports="npm" -o ./`
 * Copyright 2012-2016 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2016 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <https://lodash.com/license>
 */

/** `Object#toString` result references. */
var numberTag = '[object Number]';

/** Used for built-in method references. */
var objectProto = Object.prototype;

/**
 * Used to resolve the
 * [`toStringTag`](http://ecma-international.org/ecma-262/7.0/#sec-object.prototype.tostring)
 * of values.
 */
var objectToString = objectProto.toString;

/**
 * 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
 */
//判断一个值是否是object-like对象
function isObjectLike(value) {
  return !!value && typeof value == 'object';
}

/**
 * Checks if `value` is `NaN`.
 *
 * **Note:** This method is based on
 * [`Number.isNaN`](https://mdn.io/Number/isNaN) and is not the same as
 * global [`isNaN`](https://mdn.io/isNaN) which returns `true` for
 * `undefined` and other non-number values.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is `NaN`, else `false`.
 * @example
 *
 * _.isNaN(NaN);
 * // => true
 *
 * _.isNaN(new Number(NaN));
 * // => true
 *
 * isNaN(undefined);
 * // => true
 *
 * _.isNaN(undefined);
 * // => false
 */
//检查一个值是否是NaN
//此方法基于Number.isNaN，和全局的isNaN不一样
function isNaN(value) {
  // An `NaN` primitive is the only value that is not equal to itself.
  // Perform the `toStringTag` check first to avoid errors with some
  // ActiveX objects in IE.
  //原生的NaN只是一个自己和自己不相等的值。先执行toStringTag检查避免IE浏览器中的ActiveX对象造成的错误
  return isNumber(value) && value != +value;
}

/**
 * Checks if `value` is classified as a `Number` primitive or object.
 *
 * **Note:** To exclude `Infinity`, `-Infinity`, and `NaN`, which are
 * classified as numbers, use the `_.isFinite` method.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a number, else `false`.
 * @example
 *
 * _.isNumber(3);
 * // => true
 *
 * _.isNumber(Number.MIN_VALUE);
 * // => true
 *
 * _.isNumber(Infinity);
 * // => true
 *
 * _.isNumber('3');
 * // => false
 */
//判断一个值是否被归类为原生的number或者number对象
function isNumber(value) {
  return typeof value == 'number' ||
    (isObjectLike(value) && objectToString.call(value) == numberTag);
}

module.exports = isNaN;