1. instanceof实现判断简单类型
    2. class PrimitiveString {
    3.     static [Symbol.hasInstance](x) {
    4.         return typeof x === 'string'
    5.     }
    6. }
    7. console.log('hello' instanceof PrimitiveString)
    1. 原型链
      链接实例和原型，实现继承。
    2. 闭包
      外部函数内包裹内部函数，内部函数可以访问外部函数变量，并且外部函数上下文环境不会销毁。
    3. 手写promise
    1. const PENDING = 'pending'
    2. const RESOLVED = 'resolved'
    3. const REJECTED = 'rejected'
    5. function MyPromise(fn) {
    6.   const that = this
    7.   that.state = PENDING
    8.   that.value = null
    9.   that.resolvedCallbacks = []
    10.   that.rejectedCallbacks = []
    11.   // 待完善 resolve 和 reject 函数
    12.   // 待完善执行 fn 函数
    13.   function resolve(value) {
    14.   if (that.state === PENDING) {
    15.     that.state = RESOLVED
    16.     that.value = value
    17.     that.resolvedCallbacks.map(cb => cb(that.value))
    18.   }
    19. }
    21. function reject(value) {
    22.   if (that.state === PENDING) {
    23.     that.state = REJECTED
    24.     that.value = value
    25.     that.rejectedCallbacks.map(cb => cb(that.value))
    26.   }
    27. }
    28. try {
    29.   fn(resolve, reject)
    30. } catch (e) {
    31.   that.reject(e)
    32. }
    33. }
    35. MyPromise.prototype.then = function(onFulfilled, onRejected) {
    36.   const that = this
    37.   onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : v => v
    38.   onRejected =
    39.     typeof onRejected === 'function'
    40.       ? onRejected
    41.       : r => {
    42.           throw r
    43.         }
    44.   if (that.state === PENDING) {
    45.     that.resolvedCallbacks.push(onFulfilled)
    46.     that.rejectedCallbacks.push(onRejected)
    47.   }
    48.   if (that.state === RESOLVED) {
    49.     onFulfilled(that.value)
    50.   }
    51.   if (that.state === REJECTED) {
    52.     onRejected(that.value)
    53.   }
    54. }
    1. 手写call
    1. Function.prototype.myCall = function(context) {
    2.   if (typeof this !== 'function') {
    3.     throw new TypeError('Error')
    4.   }
    5.   context = context || window
    6.   context.fn = this
    7.   const args = [...arguments].slice(1)
    8.   const result = context.fn(...args)
    9.   delete context.fn
    10.   return result
    11. }
    1. v8垃圾回收机制
    2. 16进制 <=> rgb
    1. function hexToRGB(hex){
    2.     var hex = hex.replace("#","0x"),
    3.         r = hex >> 16,
    4.         g = hex >> 8 & 0xff,
    5.         b = hex & 0xff;
    6.     return "rgb("+r+","+g+","+b+")";
    7. }
    9. function RGBToHex(rgb){
    10.     var rgbArr = rgb.split(/[^\d]+/),
    11.         color = rgbArr[1]<<16 | rgbArr[2]<<8 | rgbArr[3];
    12.     return "#"+color.toString(16);
    13. }