JavaScript实现字典类

字典也称为映射、符号表或关联数组，在计算机科学中经常用来保存对象的引用地址。

集合以【值，值】的形式存放元素，字典是以【键，值】的形式存放元素。

class ValuePair {                             //存放一对键值的对象
    constructor(key, value) {
        this.key = key;
        this.value = value;
    }
    toString() {
        return `[#${this.key}:${this.value}]`;
    }
}


class Dictionary {
    constructor() {
        this.table = {};
    }
    toStrFn(str) {
        if (str == null) {
            return 'null';
        } else if (str === undefined) {
            return "undefined";
        } else {
            return str.toString();
        }
    }
    remove(key) {
        if (!this.hasKey(key)) {
            return false;
        }
        delete this.table[this.toStrFn(key)];
        return true;
    }
    hasKey(key) {
        return this.table[this.toStrFn(key)] != null;
    }
    set(key, value) {
        if (key == null || value == null) {
            return false;
        }
        const tableKey = this.toStrFn(key);
        this.table[tableKey] = new ValuePair(key, value);
        return true;
    }
    get(key) {
        if (!this.hasKey(key)) {
            return undefined;
        }
        return this.table[this.toStrFn(key)];  //返回值是键值对
    }
    clear() {
        this.table = {};
    }
    size() {
        return Object.keys(this.table).length;
    }
    isEmpty() {
        return this.size() === 0;
    }
    keys() {
        return this.keyValues().map(valuePair => valuePair.key);
    }
    values() {
        return this.keyValues().map(valuePair => valuePair.value);
    }
    keyValues() {
        return Object.values(this.table);
    }
    forEach(callBackFn) {
        const valuePair = this.keyValues();
        for (let i = 0; i < valuePair.length; i++) {
            callBackFn(valuePair[i].key, valuePair[i].value);
        }
    }
    toString() {
        if (this.isEmpty()) {
            return "";
        }
        const valuePair = this.keyValues();
        let objString = valuePair[0].toString();
        for (let i = 1; i < valuePair.length; i++) {
            objString = `${objString},${valuePair[i].toString()}`;
        }
        return objString;
    }
}

const dictionary = new Dictionary();

dictionary.set('Gandalf', 'gandalf@email.com');
dictionary.set('John', 'johnsnow@email.com');
dictionary.set('Tyrion', 'tyrion@email.com');

console.log(dictionary.hasKey('Gandalf')); // true
console.log(dictionary.size()); // 3

console.log(dictionary.keys()); // ["Gandalf", "John", "Tyrion"]
console.log(dictionary.values()); // ["gandalf@email.com", "johnsnow@email.com", "tyrion@email.com"]
console.log(dictionary.get('Tyrion')); // tyrion@email.com

dictionary.remove('John');

console.log(dictionary.keys()); // ["Gandalf", "Tyrion"]
console.log(dictionary.values()); // ["gandalf@email.com", "tyrion@email.com"]

console.log(dictionary.keyValues()); // [{key: "Gandalf", value: "gandalf@email.com"}, {key: "Tyrion", value: "tyrion@email.com"}]
console.log(dictionary.toString()); // [#Gandalf: gandalf@email.com],[#Tyrion: tyrion@email.com]

dictionary.forEach((k, v) => {
    console.log('forEach: ', `key: ${k}, value: ${v}`);
});
// forEach:  key: Gandalf, value: gandalf@email.com
// forEach:  key: Tyrion, value: tyrion@email.com