document.getElementsByClassName的理想实现

var

getElementsByClassName =

function

(searchClass, node,tag) {

if

(document.getElementsByClassName){

return

document.getElementsByClassName(searchClass)

}

else

{

node = node || document;

tag = tag ||

"*"

;

var

classes = searchClass.split(

" "

),

elements = (tag ===

"*"

&& node.all)? node.all : node.getElementsByTagName(tag),

patterns = [],

returnElements = [],

current,

match;

var

i = classes.length;

while

(--i >= 0){

patterns.push(

new

RegExp(

"(^|//s)"

+ classes[i] +

"(//s|$)"

));

}

var

j = elements.length;

while

(--j >= 0){

current = elements[j];

match =

false

;

for

(

var

k=0, kl=patterns.length;k<kl;k++){

match =patterns[k].test(current.className);

if

(!match)

break

;

}

if

(match)  returnElements.push(current);

}

return

returnElements;

}

}