手写call和apply

1. call 实现

(function(){
    if(!Function.prototype.call) {
      Function.prototype.call = function(context=window, ...args) {
        if(typeof this !== 'function') {
          throw new TypeError("this not a function");
      }
      context.fn = this;
      let result = context.fn(...args);
      delete context.fn;
      return result;
    }
  }
})()

1. apply 实现

(function(){
    if(!Function.prototype.apply) {
      Function.prototype.apply = function (context=window, ...args) {
        if(typeof this !== 'function') {
          throw new TypeError("this not a function");
      }
      context.fn = this;
      let result = args[0] ? context.fn(...args) : context.fn();
      delete context.fn;
      return result;
    }
  }
})()