bind,call,apply的代码实现

前言

bind，call，apply三者共同点是都可以改变函数的执行上下文，区别在于bind会返回一个新的函数，而call和apply不会返回的新的函数，而是立即执行函数。

正文

call的代码实现

Function.prototype.call = function (context) {
    context = context || window
    context.fn = this
    //let argus = [...arguments].slice(1)
    //let result = context.fn(...argus)
    let argus = []
    for(var i=1, var len=arguments.length; i<len; i++){
        argus.push('arguments['+i+']')
    }
    let result = eval('context.fn('+argus+')')
    delete context.fn
    return result
}

apply的代码实现

Function.prototype.apply = function (context, array) {
   context = context ? Object(context) : window
   context.fn = this
   let result
   if (!array) {
      result = context.fn()
   } else {
      result = context.fn(...array)
   }
   delete context.fn
   return result
}

bind的代码实现

Function.prototype.bind = function (context) {
    if (typeof this !== 'function') {
        throw new Error('please use bind by function!')
    } 
    let self = this
    let argus1 = [...arguments].slice(1)
    let fb = function () {}
    function fBind () {
        let argus2 = [...arguments]
        return self.apply(this instanceof fb ? this : context, [...argus1, ...argus2])
    }
    fb.prototype = this.prototype
    fBind.prototype = new fb()
    return fBind
}