手写 bind、call、apply

function myBind(ctx) {
  ctx.fn = this
  ctx.fn()
  delete ctx.fn
}

手写 new

function myNew(fn, ...args) {
  const obj = Object.create(fn.prototype)
  const res = fn.apply(obj, args)
  return res instanceof Object ? res : obj
}

手写 unshift

function myUnshift(...args) {
  for (let i = args.length - 1; i >= 0; i--) {
    this.splice(0, 0, args[i])
  }
  return this.length
}

实现管道函数

```js
    const pipe = (...fns) => x => fns.reduce((v, fn) => fn(v), x);
    const double = x => x * 2;
    const square = x => x * x;
    const squareDouble = pipe(double, square);
    ```