getElementById('id')getElementsByName('name')getElementsByTagName('tag')getElementById是獲取元素最快的方式,但我們不能給每個HTML元素都加以ID吧,所以我們需要一個很方便的通過className來獲取元素function getElementsByClassName(className,tagName){var ele=[],all=document.getElementsByTagName(tagName||"*");for(var i=0;i<all.length;i++){if(all[i].className==className){ele[ele.length]=all[i]; }}return ele;}console.log(getElementsByClassName("entry"));console.log(getElementsByClassName("entry","div"));

function getElementsByClassName(className,tagName){var ele=[],all=document.getElementsByTagName(tagName||"*");for(var i=0;i<all.length;i++){if(all[i].className.className.match(new RegExp('(//s|^)'+cls+'(//s|$)'))){ele[ele.length]=all[i];} }return ele;}