SOURCE

Function.prototype.myCall = function(context, ...rest) {
    context = context || window
    context.fn = this
    const res = context.fn(...rest)
    delete context.fn
    return res
}

Function.prototype.myApply = function(context, arr) {
    context = context || window
    context.fn = this
    const res = context.fn(...arr)
    delete context.fn
    return res
}

Function.prototype.myBind = function(context, ...rest1) {
    const fn = this
    return function(...rest2) {
        return fn.myCall(context, ...rest1, ...rest2)
    }
}

const person = {
    name: 'xxx',
    age: 20
}

const sayHello = function(toName) {
    console.log(`${this.name} say hello to ${toName}`)
}

sayHello.myCall(person, 'kity')
sayHello.myApply(person, ['kity'])

const fn = sayHello.myBind(person, 'kity')
fn()