字典，就是以 [键, 值] 的形式来存储元素，也常叫 映射 ， Map 。

    1. class ValuePair {
    2.     constructor(key, value) {
    3.         this.key = key;
    4.         this.value = value;
    5.     }
    7.     toString() {
    8.         return `[#${this.key}: ${this.value}]`;
    9.     }
    10. }
    11. class Dictionary {
    12.     constructor() {
    13.         this.table = {};
    14.     }
    16.     toStrFn(item) {
    17.         if (item === null) {
    18.             return 'NULL';
    19.         } else if (item === undefined) {
    20.             return 'UNDEFINED';
    21.         } else if (typeof item === 'string' || item instanceof String) {
    22.             return `${item}`;
    23.         }
    25.         return item.toString();
    26.     }
    28.     set(key, value) {
    29.         if (key != null && value != null) {
    30.             const tableKey = this.toStrFn(key);
    31.             this.table[tableKey] = new ValuePair(key, value);
    33.             return true;
    34.         }
    36.         return false;
    37.     }
    39.     remove(key) {
    40.         if (this.hasKey(key)) {
    41.             delete this.table[this.toStrFn(key)];
    42.             return true;
    43.         }
    45.         return false;
    46.     }
    48.     hasKey(key) {
    49.         return this.table[this.toStrFn(key)] ? true : false;
    50.     }
    52.     get(key) {
    53.         const valuePair = this.table[this.toStrFn(key)];
    55.         return valuePair ? valuePair.value : undefined;
    56.     }
    58.     clear() {
    59.         this.table = {};
    60.     }
    62.     size() {
    63.         return Object.keys(this.table).length;
    64.     }
    66.     isEmpty() {
    67.         return this.size() === 0;
    68.     }
    70.     keys() {
    71.         return this.keyValues().map(item => item.key);
    72.     }
    74.     values() {
    75.         return this.keyValues().map(item => item.value);
    76.     }
    78.     keyValues() {
    79.         return Object.values(this.table);
    80.     }
    82.     forEach(callback) {
    83.         const valuePair = this.keyValues();
    85.         for (let i = 0; i < valuePair.length; i++) {
    86.             const result = callback(valuePair[i].key, valuePair[i].value);
    88.             if (!result) break;
    89.         }
    90.     }
    91. }
    93. const dictionary = new Dictionary();
    95. dictionary.set('Gandalf', 'gandalf@email.com');
    96. dictionary.set('John', 'johnsnow@email.com');
    97. dictionary.set('Tyrion', 'tyrion@email.com');
    99. console.log(dictionary.get('John'))