使用javaScript实现一个字典

//因为每个键和每个键值对都设置为字符串类型，这样方便检索，所以需要写一个函数用来进行字符串转换
function defaultToString(item){
    if(item == 'null'){
        return 'null';
    }
    if(item == 'undefined'){
        return 'undefined';
    }
    if(typeof item || item instanceof String){
        return `${item}`;
    }
    return item.toString();
}
//新建一个键值对的类
class valuePair{
    constructor(key, value){
        this.key = key;
        this.value = value;
    }
    toString(){
        return `[#${this.key}:${this.value}]`;
    }
}
//新建一个字典类
class Dictionary{
    constructor(toStrFn = defaultToString){
        this.toStrFn = toStrFn;
        this.table = {};
    }
    //判断键是否存在的方法
    hasKey(key){
        return this.table[this.toStrFn(key)] != null;
    }
    //给字典添加键和键对应的键值对的方法
    set(key,value){
        const tableKey = this.toStrFn(key);
        this.table[tableKey] = new valuePair(key,value);
    }
    //根据键来获取键对应的值的方法
    get(key){
        const valuePair = this.table[this.toStrFn(key)];
        return valuePair== null?undefined:valuePair.value;
    }
    //获取当前字典的长度的方法
    size(){
        return Object.keys(this.table).length;
    }
    //判断当前字典是否为空
    isEmpty(){
        return this.size() == 0;
    }
    //获取当前字典的所有键值对
    keyValues(){
        let valuePair = [];
        for(let k in this.table){
            valuePair.push(this.table[this.toStrFn(k)]);
        }
        return valuePair;
    }
    //获取当前字典的所有键
    keys(){
        return this.keyValues().map(valuePair => valuePair.key);  
    }
    //获取当前字典的所有值
    values(){
        return this.keyValues().map(valuePair => valuePair.value);
    }
    //遍历当前字典的键值对
    forEach(callBackFn){
        let valuePairs = this.keyValues();
        for(let i = 0; i < valuePairs.length; i++){
           const result =  callBackFn(valuePairs[i].key,valuePairs[i].value);
           if(result == false){
               break;
           }
        }
    }
    //将键值对以字符串形式打印出来
    toString(){
        if(this.isEmpty()){
            return '';
        }
        let objString = `${this.keyValues()[0].toString()}`;
        let valuePairs = this.keyValues();
        for(let i = 1; i < this.size(); i++){
            objString = `${objString},${valuePairs[i].toString()}`//调用valuePair类中的toString方法
        }
        return objString;
    }
    remove(key){
        if(this.hasKey(key)){
            delete this.table[this.toStrFn(key)];
            return true;
        }
        return false;
    }
}