实现call和apply

Function.prototype.myCall = function (context) {
         var context = context || window
          console.log(context,this)
          // 给 context 添加一个属性
          // getValue.call(a, 'yck', '24') => a.fn = getValue
          context.fn = this
          // 将 context 后面的参数取出来
          var args = [...arguments].slice(1)
          // getValue.call(a, 'yck', '24') => a.fn('yck', '24')
          var result = context.fn(...args)
          // 删除 fn
          delete context.fn
          return result
}

Function.prototype.myApply = function (context) {
          var context = context || window
          context.fn = this

          var result
          // 需要判断是否存储第二个参数
          // 如果存在，就将第二个参数展开
          if (arguments[1]) {
            result = context.fn(...arguments[1])
          } else {
            result = context.fn()
          }

          delete context.fn
          return result
}