call apply bind

Function.prototype.myCall = function(context) {
  if (context === null || context === undefined) {
    context = window
  }
  context.fn = this
  const args = Array.from(arguments).slice(1)
  const result = context.fn(...args)
  delete context.fn
  return result
}
function A(a, b) {
  this.a = a
  this.b = b
  return {
    a: a,
    b: b
  }
}
A.myCall(null, 1, 2)
Function.prototype.myApply = function(context, arr = []) {
  if (context === null || context === undefined) {
    context = window
  }
  context.fn = this
  const args = arr
  const result = context.fn(...args)
  console.log(result)
  delete context.fn
  return result
}
function A(a, b) {
  this.a = a
  this.b = b
  return {
    a: a,
    b: b
  }
}
A.myApply(null, [1, 2])

Function.prototype.myBind = function(context) {
  if (context === null || context === undefined) {
    context = window
  }
  context.fn = this
  let args = Array.from(arguments).slice(1)
  return function() {
    args = [...args, ...arguments]
    return context.fn.apply(context, args)
  }

}
var obj1 = {
  a: 1,
  b: 2
}
var obj2 = {
  a: 3,
  b: 4
}
var obj3 = {
  a: 5,
  b: 6
}
function B() {
  console.log(arguments)
  console.log(this.a)
}
B.bind(obj1, 1, 2).bind(obj2, 3, 4).bind(obj3)(5, 6)
B.myBind(obj1, 1, 2).myBind(obj2, 3, 4).myBind(obj3)(5, 6)