SOURCE

function myBind(context = window) {
    let _this = this

    return function (...arg) {
        _this.call(context, ...arg)
    }
}
Function.prototype.myBind= myBind

function fun(val) {
    this.name = 'aaa'
    console.log(this.name + val)
}
let obj = {
    name: 'bbbb'
}

// fun(123)


function mycall (context = window, ...arg) {
    const _this = this
    const prototype = Symbol(1)
    context[prototype] = _this
    _this(...arg)
    delete context[prototype]
}

Function.prototype.mycall= mycall

fun.mycall(obj, 123)