call/apply/bind

均用于改变this指向。call和apply立即执行，bind延迟执行。

    let fn = function(a,b){
        console.log(this,a,b);
    }
    let obj = {name:"obj"};
    fn.call(obj,1,2)
    fn.apply(obj,[1,2])
    fn.bind(obj,1,2)

call

win.p = this this在被调用时指向调用对象

//es5
Function.prototype.newCall = function(win){
  var win = win || window;
  win.p = this;
  var newArgs = [];
  for(var i =0;i<arguments.length;i++){
    newArgs.push('arguments[' + i + ']');
  }
  var result = eval('win.p(' + newArgs + ')')
  delete win.p
  return result
}
//es6
Function.prototype.newCall = function(win,...arr){
  var win = win || window;
  win.p = this;
  var result = win.p(...arr)
  delete win.p
  return result
}

function perrson(a,b){
    return{
        name:this.name,
        a:a,b:b
    }
} 
var dog = {name:"白白"}
var bb = perrson.newCall(dog,"更快","更高")
console.log(bb) //{ name: '白白', a: '更快', b: '更高' }

apply

//es5
Function.prototype.newApply = function(win,arr){
  var win = win || window,result;
  win.p = this;
  if(!arr) {
    result = win.p()
  }else{
    var newArgs = [];
    for(var i =0;i<arr.length;i++){
      newArgs.push('arr[' + i + ']');
    }
    var result = eval('win.p(' + newArgs + ')')
  }
  delete win.p
  return result
}
//es6
Function.prototype.newApply = function(win,arr){
  var win = win || window,result;
  win.p = this;
  if(!arr) {
    result = win.p()
  }else{
    result = win.p(...arr)
  }
  delete win.p
  return result
}

function perrson(a,b){
    return{
        name:this.name,
        a:a,b:b
    }
} 
var dog = {name:"白白"}
var bb = perrson.newCall(dog,["更快","更高"])
console.log(bb) //{ name: '白白', a: '更快', b: '更高' }

bind

//es5
Function.prototype.newBind = function(win){
  if(typeof this !== "function"){
    throw new TypeError("错误")
  }
  var that = this,
      arr = Array.prototype.slice.call(arguments,1),
      o = function(){},
      newf = function (){
      var arr2 = Array.prototype.slice.call(arguments),
        arrsum = arr.concat(arr2)
      if(this instanceof o){
       that.apply(this,arrsum)
      }else{
       that.apply(win,arrsum)
      }
  }
  o.prototype = that.prototype;
  newf.prototype = new o
  return newf
}