1 == '1'  // true
1 === '1' // false

function Parent() {}
function Child() {}
Child.prototype = new Parent()

function Child() {
    Parent.call(this)
}

function Child() {
    Parent.call(this)
}
Child.prototype = Object.create(Parent.prototype)
Child.prototype.constructor = Child

class Child extends Parent {
    constructor() {
        super()
    }
}

function myInstanceof(left, right) {
    let proto = Object.getPrototypeOf(left)
    while (true) {
        if (proto === null) return false
        if (proto === right.prototype) return true
        proto = Object.getPrototypeOf(proto)
    }
}

func.call(thisArg, arg1, arg2, ...)    // 參數(shù)逐個傳遞
func.apply(thisArg, [argsArray])       // 參數(shù)作為數(shù)組傳遞
func.bind(thisArg, arg1, arg2, ...)    // 返回新函數(shù)，不立即執(zhí)行

Promise.resolve(value)     // 返回 resolved 狀態(tài)的 Promise
Promise.reject(reason)     // 返回 rejected 狀態(tài)的 Promise
Promise.all(iterable)      // 所有成功才成功，一個失敗就失敗
Promise.race(iterable)     // 第一個改變狀態(tài)的 Promise 決定結(jié)果
Promise.allSettled(iterable) // 所有 Promise 都完成后返回結(jié)果數(shù)組

class MyPromise {
    constructor(executor) {
        this.state = 'pending'
        this.value = undefined
        this.reason = undefined
        
        const resolve = (value) => {
            if (this.state === 'pending') {
                this.state = 'fulfilled'
                this.value = value
            }
        }
        
        const reject = (reason) => {
            if (this.state === 'pending') {
                this.state = 'rejected'
                this.reason = reason
            }
        }
        
        try {
            executor(resolve, reject)
        } catch (err) {
            reject(err)
        }
    }
    
    then(onFulfilled, onRejected) {
        // 簡化實現(xiàn)，實際更復(fù)雜
        if (this.state === 'fulfilled') {
            onFulfilled(this.value)
        }
        if (this.state === 'rejected') {
            onRejected(this.reason)
        }
    }
}

// 數(shù)組解構(gòu)
const [a, b] = [1, 2]

// 對象解構(gòu)
const { name, age } = { name: 'John', age: 30 }

// 函數(shù)參數(shù)解構(gòu)
function foo({ x, y }) { return x + y }

// 交換變量
[a, b] = [b, a]

// 復(fù)制數(shù)組
const arr2 = [...arr1]

// 合并數(shù)組
const arr3 = [...arr1, ...arr2]

// 函數(shù)參數(shù)
Math.max(...numbers)

// 對象淺拷貝
const obj2 = { ...obj1 }

// 支持換行
const str = `第一行
第二行`

// 支持表達(dá)式
const name = 'John'
const greeting = `Hello, ${name}!`

// 標(biāo)簽?zāi)０?
function tag(strings, ...values) {
    // strings: 模板字符串的靜態(tài)部分
    // values: 表達(dá)式的值
}

event.preventDefault()    // 阻止默認(rèn)行為
event.stopPropagation()   // 阻止冒泡
event.stopImmediatePropagation() // 阻止同一事件的其他監(jiān)聽器

// 防抖
function debounce(fn, delay) {
    let timer
    return function(...args) {
        clearTimeout(timer)
        timer = setTimeout(() => fn.apply(this, args), delay)
    }
}

// 節(jié)流
function throttle(fn, delay) {
    let lastTime = 0
    return function(...args) {
        const now = Date.now()
        if (now - lastTime >= delay) {
            fn.apply(this, args)
            lastTime = now
        }
    }
}

JSONP（僅 GET 請求）

CORS（服務(wù)器設(shè)置響應(yīng)頭）

代理服務(wù)器

postMessage

WebSocket

// 1. Set
[...new Set(array)]

// 2. filter + indexOf
array.filter((item, index) => array.indexOf(item) === index)

// 3. reduce
array.reduce((acc, cur) => acc.includes(cur) ? acc : [...acc, cur], [])

// 1. flat
arr.flat(Infinity)

// 2. reduce + 遞歸
function flatten(arr) {
    return arr.reduce((acc, cur) => 
        Array.isArray(cur) 
            ? acc.concat(flatten(cur)) 
            : acc.concat(cur), 
    [])
}

// 3. toString（僅限數(shù)字?jǐn)?shù)組）
arr.toString().split(',').map(Number)

function deepClone(obj, map = new WeakMap()) {
    if (obj === null || typeof obj !== 'object') return obj
    if (map.has(obj)) return map.get(obj)
    
    const clone = Array.isArray(obj) ? [] : {}
    map.set(obj, clone)
    
    for (let key in obj) {
        if (obj.hasOwnProperty(key)) {
            clone[key] = deepClone(obj[key], map)
        }
    }
    return clone
}

function curry(fn) {
    return function curried(...args) {
        if (args.length >= fn.length) {
            return fn.apply(this, args)
        } else {
            return function(...args2) {
                return curried.apply(this, args.concat(args2))
            }
        }
    }
}

function compose(...fns) {
    return function(x) {
        return fns.reduceRight((acc, fn) => fn(acc), x)
    }
}

function* gen() {
    yield 1
    yield 2
    return 3
}

const proxy = new Proxy(target, {
    get(target, prop) {
        return Reflect.get(target, prop)
    }
})

const name = obj?.user?.name

const value = a ?? 'default'