bind.call.apply.js

var type = "window";

const obj = {
  type: "obj",
  foo(a, b) {
    console.log("this.type", this.type, a, b);
  }
};

Function.prototype.customCall = function (context, ...restArgs) {
  context = context == null ? window : context;
  context.func = this;
  return context.func(...restArgs);
};

obj.foo.customCall(window, 1, 2);
// obj.foo.call(window, 1, 2);

Function.prototype.customApply = function (context, restArgs) {
  context = context == null ? window : context;
  context.func = this;
  return context.func(...restArgs);
};

// obj.foo.customApply(window, [1, 2]);
// obj.foo.apply(window, [1, 2]);

Function.prototype.customBind = function (context) {
  context = context == null ? window : context;

  context.func = this;
  return function anonymous(...returnArgs) {
    return context.func(...returnArgs);
  };
  // or
  // const _this = this
  // return function anonymous (...returnArgs) {
  //   return _this.call(context, ...returnArgs)
  // };
};

const bindFunc = obj.foo.customBind(window);
// bindFunc(1, 2);