js 选择器

var queryEle = function(selector){
        var selectReg = /^(#)?(\.)?(\w+)$/img;
        var result = selectReg.exec(selector),
            data = [];
        //id
        if(result[1]){
            if(result[3]){
                if(typeof document.querySelector==‘function‘){
                    return document.querySelector(result[1]+result[3]);
                }else{
                    return document.getElementById(result[3]);
                }
            }
        }else
        //class
        if(result[2]){
            if(result[3]){
                if(typeof document.getElementsByClassName==‘function‘){
                    var dom = document.getElementsByClassName(result[3]);
                    if(dom){
                        return converArr(dom);
                    }
                }else{
                    var dom2 = document.getElementsByTagName(‘*‘);
                    for(var i=0;i<dom2.length;i++){
                        if(dom2[i].className.test(new RegExp(result[2]))){
                            data.push(dom2[i]);
                        }
                    }
                }
                return data;
            }
        }else
        if(result[3]) {
            var doms = document.getElementsByTagName(result[3].toLowerCase());
            if(doms) {
                result = converArr(doms);
            }
        }
        return result;

    };
    function converArr(dom){
        var arr = null;
        try{
           arr = Array.prototype.slice.call(dom,0);
        }catch(e){
            for(var i=0;i<dom.length;i++){
                arr.push(dom[i]);
            }
        }
        return arr;
    }

    console.log(queryEle(‘.left‘));