js 手写call apply
比较麻烦的是this指向的问题,但是可以通过"对象的函数调用指向对象自身"来处理
如果没有传入context, 那么this默认指向window
Function.prototype._call = function (context) {
const type = typeof this
if (type !== "function") throw "type error: " + type
const args = [...arguments].slice(1)
context = context || window
context.fn = this
const res = context.fn(...args)
delete context.fn
return res
}
Function.prototype._apply = function (context, args) {
const type = typeof this
if (type !== "function" || !Array.isArray(args)) throw "type error"
context = context || window
context.fn = this
const res = context.fn(...args)
delete context.fn
return res
}
const fn = function () {
console.log(this, [...arguments]);
}
fn._call({ a: 1 },1,2,3,4) // {a: 1}
fn._call(null,1,2,3) // window
fn._call() // window
fn._apply({a:1},[12,23]) // {a: 1}