被作為實參傳入另一函數，并在該外部函數內被調用，用以來完成某些任務的函數，稱為回調函數。
break、return用于終止循環的區別：
- return只能用在函數體內（單獨一個for循環里直接用return會報錯）
- 對于多層循環：return直接終止，而break只是跳出所在層的循環
every
- return后的表達式為條件
- 如有一不滿足條件就停止遍歷
- 返回值是布爾值
- 可以改變this指向
- 重寫
function myEvery(callback) {var arr = this,obj = arguments[1] || window;for (var i = 0; i < arr.length; i++) {console.log(i)if (!callback.apply(obj, [arr[i], i, arr])) {return false}}return true
}
Array.prototype.myEvery = myEvery
var arr = [1, 2, 3, 4, 5]
console.log(arr.myEvery((ele) => {return ele > 1
}))
some
- 只要有一個條件滿足就停止遍歷
- 返回值是布爾值
- 可以改變this指向
function mySome(callback) {var arr = this,obj = arguments[1] || window;for (var i = 0; i < arr.length; i++) {console.log(i)if (callback.apply(obj, [arr[i], i, arr])) {return true}}return false
}
Array.prototype.mySome = mySome
var arr = [1, 2, 3, 4, 5]
console.log(arr.mySome((ele) => {return ele > 6
}))
reduce 歸納函數（重要）
- 參數1：回調函數4參數：prev | ele, index, arr
- 參數2：initVal（必傳）
- prev的初始值是initVal給的
- 每次循環可以操作prev
- 類似filter，filter是過濾，返回(return)布爾值，就往容器里放
- reduce是歸納，符合條件(if語句)就往容器里放
- reduce返回新數組nArr即回調函數內return的內容（prev）
- 和map、forEach的區別，有了一個初始值initVal
// 將url參數轉為數組形式
var qs = 'v=1&_v=j90&aip=1&a=152878233&t=pageview&_s=1&dl=https%3A%2F%2Fdeveloper.mozilla.org%2Fzh-CN%2Fdocs%2FWeb%2FJavaScript%2FReference%2FGlobal_Objects%2FJSON%2Fstringify&ul=zh-cn&de=UTF-8&dt=JSON.stringify()%20-%20JavaScript%20%7C%20MDN&sd=24-bit&sr=1536x864&vp=1519x182&je=0&_u=QACAAAABAAAAAC~&jid=1406847847&gjid=1261334307&cid=1705225672.1581390240&tid=UA-36116321-5&_gid=1728790607.1622245970&_r=1&_slc=1&z=575736183'
var arr = qs.split('&')
var nArr = arr.reduce(function (prev, ele) {qArr = ele.split('=')prev[qArr[0]] = qArr[1]return prev
}, {})
console.log(nArr)
- 重寫
function myReduce(callback, initVal) {var arr = this;var obj = arguments[2] || windowvar nResvar prevfor (var i = 0; i < arr.length; i++) {prev = i === 0 ? initVal : nResnRes = callback.apply(obj, [prev, arr[i]])}return nRes
}
Array.prototype.myReduce = myReduce
var qs = 'v=1&_v=j90&aip=1&a=152878233&t=pageview&_s=1&dl=https%3A%2F%2Fdeveloper.mozilla.org%2Fzh-CN%2Fdocs%2FWeb%2FJavaScript%2FReference%2FGlobal_Objects%2FJSON%2Fstringify&ul=zh-cn&de=UTF-8&dt=JSON.stringify()%20-%20JavaScript%20%7C%20MDN&sd=24-bit&sr=1536x864&vp=1519x182&je=0&_u=QACAAAABAAAAAC~&jid=1406847847&gjid=1261334307&cid=1705225672.1581390240&tid=UA-36116321-5&_gid=1728790607.1622245970&_r=1&_slc=1&z=575736183'
var arr = qs.split('&')
var nRes = arr.myReduce(function (prev, ele) {qArr = ele.split('=')prev[qArr[0]] = qArr[1]console.log(this)return prev
}, {}, { name: 'this' })
console.log(nRes)
reduceRight
- 從最后一個開始倒著遍歷，和reduce的順序相反
function myReduce(callback, initVal) {var arr = this;var obj = arguments[2] || windowvar nResvar prevfor (var i = 0; i < arr.length; i++) {prev = i === 0 ? initVal : nResnRes = callback.apply(obj, [prev, arr[i], i, arr])}return nRes
}
Array.prototype.myReduce = myReduce
Array.prototype.myReduceRight = function (callback, initVal) {var arr = this;var obj = arguments[2] || windowfor (var i = arr.length - 1; i >= 0; i--) {initVal = callback.apply(obj, [initVal, arr[i], i, arr])}return initVal
}
var arr = [1, 2, 3, 4, 5]
var nRes1 = arr.myReduce(function (prev, ele, index, arr) {prev.push(index + ':' + ele)return prev
}, [])
console.log(nRes1)
var nRes2 = arr.myReduceRight(function (prev, ele, index, arr) {prev.push(index + ':' + ele)return prev
}, [])
console.log(nRes2)
練習
- 實現模糊搜索
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><input type="text" id="J_searchInput" placeholder="請輸入小說"><ul class="J_list"><span>暫無數據</span></ul><div id="J_data" style="display: none;">[{"id":1,"name":"飛狐外傳","chargeFlag":0},{"id":2,"name":"雪山飛狐","chargeFlag":0},{"id":3,"name":"連城訣","chargeFlag":0},{"id":4,"name":"天龍八部","chargeFlag":1},{"id":5,"name":"射雕英雄傳","chargeFlag":1},{"id":6,"name":"白馬嘯西風","chargeFlag":0},{"id":7,"name":"鹿鼎記","chargeFlag":1}]</div><script type="text/html" id="J_tpl"><li>{{name}}</li></script><script>; (function (document) {var oInput = document.getElementById('J_searchInput')var data = JSON.parse(document.getElementById('J_data').innerHTML)var tpl = document.getElementById('J_tpl').innerHTML;var list = document.getElementsByClassName('J_list')[0]var emptyTpl = list.innerHTMLvar init = function () {bindEvent()}function bindEvent() {oInput.addEventListener('input', inputBlur, false)}function inputBlur(e) {// console.log(this.value) // 這就可以獲取valuevar e = e || window.event;var tar = e.target || e.srcElement;var tagName = tar.tagName.toLowerCase()if (tagName === 'input') {var foundNames = searchByName(tar.value)list.innerHTML = renderList(foundNames)}}function searchByName(key) {if (!key) {return []}return data.reduce(function (prev, ele) {// 模糊搜索var name = ele.namename.includes(key) ? prev.push(ele) : ''return prev}, [])}function renderList(data) {if (data.length === 0) {return emptyTpl}var list = ''data.forEach((item) => {list += tpl.replace(/{{(.*?)}}/g, function (node, key) {return {name: item.name}[key]})})return list}init()})(document)</script>
</body></html>
密鑰加密系統、數字簽名、數字證書的一些概念)
