call、apply、bind的极简实现

Copy 
1Function.prototype.call = function (context, args) {
2  let symbolFn = Symbol("fn");
3  symbolFn = this;
4  context[symbolFn](args);
5  delete context[symbolFn];
6};

Copy 
1Function.prototype.apply = function (context, args) {
2  let symbolFn = Symbol("fn");
3  symbolFn = this;
4  context[symbolFn](...args);
5  delete context[symbolFn];
6};

Copy 
1Function.prototype.bind = function (context) {
2  let symbolFn = Symbol("fn");
3  symbolFn = this;
4  return function () {
5    let result = context[symbolFn](...arguments);
6    delete context[symbolFn];
7    return result;
8  };
9};