Handwritten implementation of call, apply, bind

preparation

First, define the show function to print the name attribute and parameters in the specified object;

function show(...args) {
    console.log(this.name);
    console.log(args);
}

Define the object, which contains the name attribute

let obj = {
    name:'philip'
}

Define function, convenient to call

    function mycall(fn, object, ...args) {
        return fn._call(object, ...args)
    }

    function myapply(fn, object, array) {
        return fn._apply(object, array)
    }

    function mybind(fn , object , ...args){
        return fn._bind(object,...args)
    }

call

As a prototype property of a function, it needs to be mounted on the function prototype
The first parameter is the object, and the second parameter is any number of parameters

Function.prototype._call = function (obj,...args) {

}

Add attributes to the object. The type is the function that currently uses the call method
Call the function, delete the function attribute after calling to make space

Function.prototype._call = function (obj,...args) {
    obj.fn = this // Add attributes to the object. The type is the function that currently uses the call method
    obj.fn(...args) // Call the function
    delete obj.fn // delete the function attribute after calling to make space
}

apply

It has the same function as the call method, but the second parameter needs to be an array

Function.prototype._apply = function (obj,args=[]) {
    if(args && !(args instanceof Array)){
        throw new Error("TypeError:apply only receive array")
    }
    obj.fn = this
    obj.fn(...args)
    delete obj.fn
}

bind

The bind method returns a function that can receive any parameter

Function.prototype._bind = function (obj, ...args1) {
        return (...args2) => {
            obj.fn = this
            obj.fn(...args1.concat(...args2))
            delete obj.fn
        }
    }

test

mycall(show, obj, 'a', 'b', 'c') // philip ['a','b','c']
myapply(show, obj, ['a', 'b', 'c']) // philip ['a','b','c']
let result = mybind(show,obj,'a', 'b');result('c')// philip ['a','b','c']