深入探究數組常用API學習筆記（一）

• 仿寫Array.prototype.forEach

  	// [].forEach((elem, index, array) => {})
  	Array.prototype.forEach = function (func) {
  		for (var i = 0, len = this.length; i < len; i ++) {
  			func(this[i], i, this)
  		}
  	}
  	// 所以forEach的回調函數中不支持break
  

• 仿寫Array.prototype.filter

  	// [].filter((elem, index, array) => {})
  	Array.prototype.filter = function (func) {
  		var res = []
  		for (var i = 0, len = this.length; i < len; i ++) {
  			if (func(this[i], i, this)) {
  				res.push(this[i])
  			}
  		}
  		return res
  	}
  

• 仿寫Array.prototype.map

  	// [].map((item, index, array) => {})
  	Array.prototype.simpleMap = function (func) {
  		var res = []
  		for (var i = 0, len = this.length; i < len; i ++) {
  			// 【注意】: 這是淺拷貝
  			res.push(func(this[i], i, this))
  		}
  		return res
  	}
  
  	Array.prototype.deepMap = function (func) {
  		var res = []
  		for (var i = 0, len = this.length; i < len; i ++) {
  			// 【注意】: 這是深拷貝
  			let newItem = func(deepClone(this[i]), i, this)
  			res.push( newItem )				
  		}
  		return res
  	}
  
  	function _deepClone(origin) {
  		// 原始值直接返回
  		if (typrof(origin) !== 'object' || origin == null) {
  			return origin
  		}
  
  		// 初始化克隆結果
  		let cloneObj
  		if (origin instanceof Array) { cloneObj = [] }
  		if (origin instanceof Object) { cloneObj = {} }
  		
  		// 對於引用值遍歷克隆
  		for (let key in origin) {
  			if (Object.hasOwnProperty(key)) {
  				cloneObj[key] = deepClone(origin[key])
  			}
  		}
  
  		// 返回克隆結果
  		return clone
  	}