Native html element selector is similar to jquery selector_javascript skills

To do the front-end, you need to select elements. Although jquery and major js libraries have helped me build the wheel, I want to try to implement one myself. It happens that the project is not busy, so I just add it to my own js file, as follows is the implementation code. It can be called using the format $g("#content .op"), which is the same as the parameters of jquery $():

function $findChilds(parentNode, text) 
{ 
//如果不传入父节点的话，默认为body 
if(parentNode == undefined) 
parentNode = document.body; 
var childNodes = parentNode.childNodes; 
var results = []; 
//子节点大于零才循环 
if(childNodes.length > 0) 
{ 
var length = childNodes.length; 
//循环查找符合text的节点 
for(var i=0;i<length;++i) 
{ 
//三种情况，className，id， tagName 
switch(text.substr(0, 1)) 
{ 
case '.': 
//这两种:parentNode.getElementsByClassName,parentNode.all 
//都是后来加上的，如果浏览器这两种方法都不支持，那就只能暴力递归了 
if(parentNode.getElementsByClassName) 
return parentNode.getElementsByClassName(text.substr(1)); 
else if(parentNode.all) 
{ 
var finded = []; 
var jlength = parentNode.all.length; 
for(var j=0;j<jlength;++j) 
if(parentNode.all[j].className == text.substr(1)) 
finded.push(parentNode.all[j]); 
return finded; 
} 
//以上两种方法都不支持，直接判断 
if(childNodes[i].className == text.substr(1)) 
results.push(childNodes[i]); 
break; 
case '#': 
return [document.getElementById(text.substr(1))]; 
default: 
return parentNode.getElementsByTagName(text); 
} 
//判断完后，把当前子元素的子元素传入$findChilds进行递归查找，返回的结果直接和现在的结果合并 
results = results.concat($findChilds(childNodes[i], text)); 
} 
} 
return results; 
} 

String.prototype.vtrim = function() { 
return this.replace(/^\s+|\s+$/g, ''); 
} 

function $g(text) 
{ 
//按照空格分割参数 
var values = text.vtrim().split(" "); 
var length = values.length; 
//如果只有一个选择参数的话，就直接调用dom方法返回结果。 
if(length == 1) 
switch(values[0].substr(0, 1)) 
{ 
case "#": 
return document.getElementById(values[0].substr(1)); 
case ".": 
if(document.getElementsByClassName) 
return document.getElementsByClassName(values[0].substr(1)); 
default: 
return document.getElementsByTagName(values[0]); 
} 
//每次迭代都会产生许多符合参数的结果节点,这里结果节点的名称为parentNodes，第一次循环默认为body 
var parentNodes = [document.body]; 
//外层循环为迭代每个传入的参数 
for(var i = 0; i < length; ++i) 
{ 
var jlength = parentNodes.length; 
var results = []; 
//这里如果values的长度为零的话， 
//就说明是多出来的空格， 
//例如:$g(" .content");这种情况不执行代码直接跳入下一循环 
var tmpValue = values[i].vtrim(); 
if(tmpValue.length <= 0) 
continue; 
//内层循环为迭代每个结果节点， 
//在结果节点中查找符合选择条件的结果。当然第一次为body 
for(var j=0;j<jlength;++j) 
{ 
//$findChilds就是上边的那个函数，就是选择某个节点的子节点的 
var result = $findChilds(parentNodes[j], values[i].vtrim()); 
var rlength = result.length; 
//因为返回的有时候是html容器，无法直接和数组concat所以倒入数组，这里有优化空间，但暂不考虑性能先这么做 
for (var k = 0; k < rlength; ++k) 
results.push(result[k]); 
} 
//没有结果，立即返回undefined 
if(results == undefined || results.length <= 0) 
return undefined; 
//最后一次循环就直接返回结果数组，但是如果最后一个选择条件是选择id的话，那就不返回数组直接返回dom对象了 
if (i == length - 1) 
{ 
if (values[i].substr(0, 1) == "#") 
return results[0]; 
return results; 
} 
parentNodes = results; 
} 
}

After testing under ff ie6, simply selecting the ID is much faster than jquery,
The few other partial selection modes I've tested are faster than jquery.
Of course, the test cannot be comprehensive, and there may be bugs, and it does not support pseudo-class selections like .content:first-child.