1. instanceof
function myInstanceof (L, R) {
if (L === null || typeof L !== 'object') return false
let proto = Object.getPrototypeOf(L)
// 可以换成
// let proto = L.__proto__
while (true) {
if (proto === null) return false
if (proto === R.prototype) return true
proto = Object.getPrototypeOf(proto);
}
}
// 测试代码：
let Car = function() {};
let BM = new Car();
console.log(myInstanceof(BM, Car)) // true
2.对象的深复制
function deepClone(source) {
let parents = [];
let children = [];
function getRegExp(reg) {
let result = "";
if (reg.ignoreCase) {
result += "i";
}
if (reg.global) {
result += "g";
}
if (reg.multiline) {
result += "m";
}
return result;
}
function _clone(parent) {
if (parent === null) return null;
if (typeof parent !== "object") return parent;
var child, proto;
if (Object.prototype.toString.call(parent) === "[object Array]") {
child = [];
} else if (Object.prototype.toString.call(parent) === "[object RegExp]") {
child = new RegExp(parent.source, getRegExp(parent));
if (parent.lastIndex) children.lastIndex = parent.lastIndex;
} else if (Object.prototype.toString.call(parent) === "[object Date]") {
child = new Date(parent.getTime());
} else {
// 处理对象原型
proto = Object.getPrototypeOf(parent);
child = Object.create(proto);
}
// 处理循环引用
var index = parents.indexOf(parent);
if (index !== -1) {
// 如果父数组存在本对象, 说明之前已经被引用过，直接返回此对象
return children[index];
}
parents.push(parent);
children.push(child);
for (const key in parent) {
if (Object.hasOwnProperty.call(parent, key)) {
child[key] = _clone(parent[key]);
}
}
return child;
}
return _clone(source);
}
var origin = {
a: 1,
b: [2, 3, 4],
c: {
d: "xiaoxiang",
},
e: new RegExp("\d", "g"),
f: new Date(),
g: function () {
console.log(this.a);
},
};
origin.h = origin;
var reslut = deepClone(origin);
console.log(origin);
reslut.b.push(5);
reslut.c.d = "jjjjj";
console.log(reslut);
3.冒泡排序
function sortA(arr) {
for (var i = 0; i < arr.length - 1; i++) {
for (var j = i + 1; j < arr.length; j++) {
if (arr[i] > arr[j]) {
var index = arr[j];
arr[j] = arr[i];
arr[i] = index;
}
}
}
return arr;
}
//demo：
var numarr = [12, 18, 20, 19, 33, 9, 10, 6];
console.log(sortA(numarr)); //[6, 9, 10, 12, 18, 19, 20, 33]
4.快速排序
function sortB(arr) {
if (arr.length <= 1) {
return arr;
} else {
var len = Math.floor(arr.length / 2);
var middlenum = arr.splice(len, 1);
var left = [];
var right = [];
for (var i = 0; i < arr.length; i++) {
if (arr[i] < middlenum) {
left.push(arr[i]);
} else {
right.push(arr[i]);
}
}
}
return sortB(left).concat(middlenum, sortB(right));
}
//demo：
console.log(sortB([12, 16, 20, 9, 8, 17, 10, 23])); //[8, 9, 10, 12, 16, 17, 20, 23]
5. 节流和防抖函数
<!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>节流和防抖函数</title>
</head>
<style>
#box {
width: 200px;
height: 5000px;
background-color: orange;
}
</style>
<body>
<input type="text" id="testInput" />
<div id="box"></div>
<script>
/**
* 节流
* 常用的场景： window.resize window.onScroll onMouseMove 等等
* */
function jieliu(fn, text) {
let canRun = true;
return () => {
if (canRun) {
canRun = false;
setTimeout(() => {
fn(text);
canRun = true;
}, 1000);
}
};
}
function myfn(val) {
console.log(1, val);
}
window.addEventListener("scroll", jieliu(myfn, "hhhh"));
/**
* 防抖
* 常用的场景：input 输入
* */
function fangdou(fn) {
let timer = null;
return function () {
if (timer) {
clearTimeout(timer);
}
timer = setTimeout(() => {
fn();
}, 300);
};
}
function myfn2() {
console.log("要请求了");
}
document.getElementById("testInput").oninput = fangdou(myfn2);
// document.getElementById("testInput").addEventListener("input", fangdou(myfn2))
</script>
</body>
</html>
6.斐波那契数列 ( 1,1,2,3,5,8... )
function digui(index) {
if (index < 0) {
return 0;
}
if (index <= 2) {
return 1;
}
return digui(index - 1) + digui(index - 2);
}
//demo：
console.log(digui(5)); //5
7.数组去重
7.1 利用对象的键不能相同去重
function norepeat(arr) {
var obj = {},
newarr = [];
for (var i = 0; i < arr.length; i++) {
if (!obj[arr[i]]) {
obj[arr[i]] = 1;
newarr.push(arr[i]);
}
}
return newarr;
}
console.log(norepeat([1, 2, 1, 2, 3, 3, 1, 2])); //[1,2,3]
7.2 数组排序后相邻去除法
function loop(arr) {
arr.sort();
var newarr = [arr[0]];
for (var i = 0; i < arr.length; i++) {
if (arr[i] !== newarr[newarr.length - 1]) {
newarr.push(arr[i]);
}
}
return newarr;
}
console.log(loop([1, 4, 3, 1, 2, 3, 3, 1, 2])); //[1,2,3,4]
7.3 遍历数组用indexOf去重
function fn1(arr) {
var newarr = [];
for (var i = 0; i < arr.length; i++) {
if (newarr.indexOf(arr[i]) == -1) {
newarr.push(arr[i]);
}
}
return newarr;
}
console.log(fn1([1, 4, 3, 1, 2, 3, 3, 1, 2])); //[1, 4, 3, 2]
7.4 ES6提供的方法set
var newa = Array.from( new Set( [1, 4, 3, 1, 2, 3, 3, 1, 2]) );
console.log(newa);//[1, 4, 3, 2]
var newb = [...new Set( [1, 4, 3, 1, 2, 3, 3, 1, 2] )];
console.log(newb); //[1, 4, 3, 2]
8 阶乘 fn(5) = 54321
function fn(n) {
if (n < 2) {
return n;
}
return n * fn(n - 1);
}
console.log(fn(5));
