细说(值传递、引用传递)的区别, 数组和对象解构的常用方法, call.apply.bind的区别与联系, 访问器属性的原理与实现
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2022-03-06 13:38:33
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值传递与引用传递的区别与联系:
深拷贝:值传递: 原始类型,string,number,bool引用传递: 引用类型,object,array浅拷贝: 引用传递入参:调用函数是传入的参数,简称:"入参"
样式代码:
<script>let a = 1; //赋值、值传递:原始类型,string,number,boolconsole.log("a = %d, b = %d", a, b);a = 2;console.log("a = %d, b = %d", a, b); //更新a,不影响blet obj1 = { a: 1, b: 2 }; //引用传递:引用类型,object,arrayconsole.log(obj1);let obj2 = obj1;console.log(obj2);obj1.a = 10; // 更新obj1console.log(obj1);console.log(obj2); //obj2同步更新const f1 = (x) => (x = 10); //传参时,不论什么类型,都是"值传递"let m = 5;console.log("m = %d", m);f1(m);console.log("m = %d", m); //函数中对参数的更新,并不会影响到入参const f2 = (x) => (x.a = 10);let o = { a: 1, b: 2 };console.log(o);f2(o);console.log(o); //看上去函数中对于o.a的更新生效,实际上仍是值传递const obj = { x: 1, y: 2 }; //对于引用类型,只有全新赋值才算是更新,修改属性不算的obj.x = 20;const f3 = (x) => (x = {}); // 赋值一个全新对象,才是更新f3(o);console.log(o); // 函数中对于对象/引用参数的更新并没有影响到入参</script>
效果预览:
数组和对象解构的常用方法与函数传数:
解构赋值: 快速从集合数据(数组/对象解构出独立变量)
<script>let [a, b, c] = [1, 2, 3]; //数组console.log(a, b, c);[a, b] = [1, 2, 3];console.log(a, b);[a, b, c, d = "xxxx"] = [1, 2, 3];console.log(a, b, c, d);[a, b, ...c] = [1, 2, 3, 4, 5];console.log(a, b, c);[, , a, ,] = [1, 2, 3, 4, 5];console.log(a);let x = 1,y = 2,t;console.log("x = %d, y = %d", x, y);[y, x] = [x, y];console.log("x = %d, y = %d", x, y);let { id, name } = { id: 10, name: "手机" }; //对象解构console.log(id, name);({ name, id } = { id: 10, name: "手机" }); //属性名与变量名必须一一对应,顺序无所谓console.log(id, name);let email = "admin@php.cn";let { role, email: userEmail } = { role: "user", email: "user@php.cn" };console.log(userEmail);console.log(email);//参数解构let sum = ([a, b]) => a + b; //数组传参console.log(sum([10, 20]));let getUser = ({ name, email }) => [name,email]; // 对象传参console.log(getUser({ email: "tp@php.cn", name: "老师" }));</script>
效果预览:
bind,call,apply的区别与联系:
bind()不会立即执行,只返回一个函数声明call/apply立即执行
样式代码:
<body><button>click</button><script>function hello(name) {this.name = name;console.log(this.name);}const obj = { name: "admin" };//经典调用console.log(hello("朱老师"));//bind()不会立即执行let f = hello.bind(obj, "天蓬老师");console.log(f());//call/apply立即执行f = hello.call(obj, "灭绝老师");console.log(f);f = hello.apply(obj, ["西门老师"]);console.log(f);</script></body>
效果预览:
访问器属性的原理与实现过程:
将方法伪造成一个属性
样式代码:
<script>const product = {data: [{ name: "电脑", price: 5000, num: 5 },{ name: "手机", price: 4000, num: 10 },{ name: "电视", price: 9000, num: 4 },],get total() { // 将方法伪造成一个属性return this.data.reduce((t, c) => (t += c.price * c.num), 0);},set setPrice(price) {this.data[1].price = price;},};console.log("总金额 :", product.total);console.log(product.data[1].price);product.setPrice = 9988;console.log(product.data[1].price);</script>
访问器属性的优先级:
访问器属性优先级高于同名的普通属性
<script>let user = {data: { name },get name() {return this.data.name;},set name(value) {this.data.name = value;},};user.name = "今天天气真不错";console.log(user.name);</script>
多分支与swithc转换的技巧:
score = 90; //多分支if (score >= 60 && score < 80) {console.log("合格");} else if (score >= 80 && score <= 100) {console.log("学霸");}else if (score > 100 || score < 0) { // 判断成绩是否合法console.log("非法数据");} else {console.log("补考吧");}score = 90; //switch来简化多分支时,switch是严格匹配switch (true) {case score >= 60 && score < 80:console.log("合格");break;case score >= 80 && score <= 100:console.log("学霸");break;case score > 100 || score < 0: //判断成绩是否合法console.log("非法数据");break;default:console.log("补考吧");}let response = "Success"; // switch用在单值判断switch (response.toLocaleLowerCase()) {case "fail":console.log("请求失败");break;case "success":console.log("请求成功");break;default:console.log("未知错误");}</script>
效果预览:
三元运算符:
简化双分支:条件? true : false如果为真执行第一个分支,如果为假执行第二个分支,三元运算符会将：右边的视为一个整体，其优先级应该是很低的，如果要先求三元运算符中的顺，必须先将其用括号括起来：
<script>//双分支score = 60;console.log(score >= 60 ? "及格" : "补考吧");</script>
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