let obj1 = {
      name: '123',
      getName: function () {
        return this.name
      }
    }

    let obj2 = {
      name: '456'
    }

    console.log(obj1.getName())  // 123
    console.log(obj1.getName.call(obj2)) // 456

    Function.prototype.myCall = function (context = window) {
      let args = Array.from(arguments).splice(1)
      if (typeof this !== 'function') return
      // 关键在于利用对象的特性，直接在将函数指向新的对象，并指向该函数
      !context.__fn__ && context.__fn__ = this
      let res = context.__fn__(...args)
      // 删除该对象上的属性
      delete context.__fn__

      return res
    }

    console.log(obj1.getName.myCall(obj2))  // 456