详解es6Map实现原理及实现自己的Map方法

男娘i 2021-09-20 06:38 271阅读 0赞

//Map
            //1.不重复
            //2.字符串 对象 NaN null [] function(){} 10
            //3.set get delete has clear方法
    
            function myMap() {
                this.bucketLength = 8;
                this.init();
            }
    
            myMap.prototype.init = function () {
                // 初始化 桶 8
                this.bucket = new Array(this.bucketLength);
                for (var i = 0; i < this.bucket.length; i++) {
                    this.bucket[i] = {
                        type: 'bucket_' + i,
                        next: null
                    }
                }
            }
            // 
            // 1. [0, 8)
            // 2. 重复算值固定
            myMap.prototype.makeHash = function (key) {
                let hash = 0;
                // string   
                if (typeof key !== 'string') {
                    if (typeof key == 'number') {
                        //number NaN 
                        hash = Object.is(key, NaN) ? 0 : key;
                    } else if (typeof key == 'object') {
                        // null {} []
                        hash = 1;
                    } else if (typeof key == 'boolean') {
                        // true false boolean
                        hash = Number(key);
                    } else {
                        // undefined  function(){}
                        hash = 2;
                    }
                } else {
                    // string
                    // 'a' 'ab' 'asdasdadasda';
                    // 长度大于等于3 前三个字符 ascii 累加 
                    for (let i = 0; i < 3; i++) {
                        // key[]
                        hash += key[i] ? key[i].charCodeAt(0) : 0;
                    }
                }
                return hash % 8;
            }
    
            myMap.prototype.set = function (key, value) {
                let hash = this.makeHash(key);
                let oTempBucket = this.bucket[hash];
                while (oTempBucket.next) {
                    if (oTempBucket.next.key == key) {
                        oTempBucket.next.value = value;
                        return;
                    } else {
                        oTempBucket = oTempBucket.next;
                    }
                };
                oTempBucket.next = {
                    key: key,
                    value: value,
                    next: null
                };
            }
    
            myMap.prototype.get = function (key) {
                let hash = this.makeHash(key);
                let oTempBucket = this.bucket[hash];
                while (oTempBucket) {
                    if (oTempBucket.key == key) {
                        return oTempBucket.value;
                    } else {
                        oTempBucket = oTempBucket.next;
                    }
                }
                return undefined;
            }
    
            myMap.prototype.delete = function (key) {
                let hash = this.makeHash(key);
                let oTempBucket = this.bucket[hash];
                while (oTempBucket.next) {
                    if (oTempBucket.next.key == key) {
                        oTempBucket.next = oTempBucket.next.next;
                        return true;
                    } else {
                        oTempBucket = oTempBucket.next;
                    }
                }
                return false;
            }
    
            myMap.prototype.has = function (key) {
                let hash = this.makeHash(key);
                let oTempBucket = this.bucket[hash];
                while (oTempBucket) {
                    if (oTempBucket.next && oTempBucket.next.key == key) {
                        return true;
                    } else {
                        oTempBucket = oTempBucket.next;
                    }
                }
                return false;
            };
    
            myMap.prototype.clear = function (key) {
                this.init();
            };