Function.prototype.bind=function(ctx){
    let fn = this;
    
    if(!ctx){
        ctx = typeof window !== 'undefined' ? window : global;
    }
    
    return function(...args){
        ctx.fn=fn;
        ctx.fn(...args)
    }
}

function f(){
    console.log(this.name);
}

var o = {name: 'o'};
var b = {name: 'b'};

f.bind(o)();
f.bind(b)();