JavaScript基础之运算符与表达式详解

1 == 1        // 返回 true 
1 == '1'    // 返回 true，会先将右侧的字符串转为数字，再做比较
1 === '1'    // 返回 false，类型不等，直接返回 false

typeof 1    // 返回 'number'
typeof '1'    // 返回 'string'

function test(n = '男') {
    console.log(n);
}

function test(n) {
    if(n === undefined) {
        n = '男';
    }
    console.log(n);
}

function test(n) {
    n = (n === undefined) ? '男' : n;
    console.log(n);
}

function test(n) {
    n = n || '男';
    console.log(n);
}

function test(n) {
    if(n === undefined || n === null) {
        n = '男';
    }
    console.log(n);
}

function test(n) {
    n = n ?? '男';
    console.log(n);
}

let stu1 = {
    name:"张三",
    address: {
        city: '北京'
    }
};
 
let stu2 = {
    name:"李四"
}
 
let stu3 = {
    name:"李四",
    address: null
}

function test(stu) {
    console.log(stu.address.city)
}

function test(stu) {
    console.log(stu.address?.city)
}

function test(stu) {
    if(stu.address === undefined || stu.address === null) {
        console.log(undefined);
        return;
    }
    console.log(stu.address.city)
}

let arr = [1,2,3];
 
function test(a,b,c) {
    console.log(a,b,c);
}

let arr1 = [1,2,3];
let arr2 = [...arr1];        // 复制数组

let obj1 = {name:'张三', age: 18};
 
let obj2 = {...obj1};        // 复制对象

let o1 = {name:'张三', address: {city: '北京'} }
 
let o2 = {...o1};

let a1 = [1,2];
let a2 = [3,4];
 
let b1 = [...a1,...a2];        // 结果 [1,2,3,4]
let b2 = [...a2,5,...a1]    // 结果 [3,4,5,1,2]

let o1 = {name:'张三'};
let o2 = {age:18};
let o3 = {name:'李四'};
 
let n1 = {...o1, ...o2};    // 结果 {name:'张三',age:18}
 
let n2 = {...o3, ...o2, ...o1}; // 结果{name:'李四',age:18}

let arr = [1,2,3];
 
let [a, b, c] = arr;    // 结果 a=1, b=2, c=3

let arr = [1,2,3];
 
function test([a,b,c]) {
    console.log(a,b,c)     // 结果 a=1, b=2, c=3
}
 
test(arr);    

let obj = {name:"张三", age:18};
 
let {name,age} = obj;    // 结果 name=张三, age=18

let obj = {name:"张三", age:18};
 
function test({name, age}) {
    console.log(name, age); // 结果 name=张三, age=18
}
 
test(obj)