原生dom 模拟jquery hasclass

var hasClass = (function(){
var div = document.createElement("div") ;
if( "classList" in div && typeof div.classList.contains === "function" ) {
return function(elem, className){
return elem.classList.contains(className) ;
} ;
} else {
return function(elem, className){
var classes = elem.className.split(/\s+/) ;
for(var i= 0 ; i < classes.length ; i ++) {
if( classes[i] === className ) {
return true ;
}
}
return false ;
} ;
}
})() ;

alert( hasClass(document.documentElement, "no-js") ) ;