jquery dollar sign selector in plain js

jquery-selector.js

window.$ = function(selector) {
    var selectorType = 'querySelectorAll';

    if (selector.indexOf('#') === 0) {  //if id selector
        selectorType = 'getElementById';
        selector = selector.substr(1, selector.length);
    }
    return document[selectorType](selector);
};

//usage:
var id_el = $('#id_selector');      //return one object
var cls_el = $('.class_selector');  //return array object

id_el.style.fontSize = '100px'; //correct
//cls_el.style.fontSize = '100px'; //incorrect
cls_el[0].style.fontSize = '100px'; //correct