正则表达式--子表达式

一个很好的正则子表达式的例子。

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1	var reg = /^(#)?(\.)?(\w+)$/img;//包含了3个子表达式。

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var query = function(selector) {        var reg = /^(#)?(\.)?(\w+)$/img;        var regResult = reg.exec(selector);        var result = [];        //如果是id选择器        if(regResult[1]) {            if(regResult[3]) {                if(typeof document.querySelector === "function") {                    result.push(document.querySelector("#"+regResult[3]));                }                else {                    result.push(document.getElementById(regResult[3]));                }            }        }        //如果是class选择器        else if(regResult[2]) {            if(regResult[3]) {                if(typeof document.getElementsByClassName === 'function') {                    var doms = document.getElementsByClassName(regResult[3]);                    if(doms) {                        result = converToArray(doms);                    }                }                //如果不支持getElementsByClassName函数                else {                    var allDoms = document.getElementsByTagName("*") ;                    for(var i = 0, len = allDoms.length; i < len; i++) {                        if(allDoms[i].className.search(new RegExp(regResult[2])) > -1) {                            result.push(allDoms[i]);                        }                    }                }            }        }        //如果是标签选择器        else if(regResult[3]) {            var doms = document.getElementsByTagName(regResult[3].toLowerCase());            if(doms) {                result = converToArray(doms);            }        }        return result;    };      function converToArray(nodes){        var array = null;        try{            array = Array.prototype.slice.call(nodes,0);//针对非IE浏览器        }catch(ex){            array = new Array();            for( var i = 0 ,len = nodes.length; i < len ; i++ ) {                array.push(nodes[i])            }        }        return array;    }