JavaScript: util getElementsByClassName

getElementsByClassName.js

/*
 * @name [getElementsByClassName]
 * @overview [根据元素clsssName得到元素集合]
 * @param {[string]}   fatherId 	[父元素的ID，默认为document]
 * @param {[string]}	tagName 	[子元素的标签名]
 * @param {[string]}	className 	[用空格分开的className字符串]
 *
 * @author unknown
 */
function getElementsByClassName(fatherId,tagName,className){
    var node = fatherId&&document.getElementById(fatherId) || document;
	if(node.getElementsByClassName){
	    return node.getElementsByClassName(className);
	}
    tagName = tagName || "*";
    className = className.split(" ");
    var classNameLength = className.length;
    for(var i=0,j=classNameLength;i<j;i++){
        //创建匹配类名的正则
        className[i]= new RegExp("(^|\\s)" + className[i].replace(/\-/g, "\\-") + "(\\s|$)"); 
    }
    var elements = node.getElementsByTagName(tagName);
    var result = [];
    for(var i=0,j=elements.length,k=0;i<j;i++){//缓存length属性
        var element = elements[i];
        while(className[k++].test(element.className)){//优化循环
            if(k === classNameLength){
                result[result.length] = element;
                break;
            }   
        }
        k = 0;
    }
    return result;
}