addClass的實現

function?addClass(elem,value)?{

????var?classes,?cur,?clazz,?j,?finalValue
????//?如果參數是多個樣式設置"blue?highlight?under"按照\/S+\g空格分割
????classes?=?(value?||?"").match(/\S+/g)?||?[];
????var?classNameStr='';
????for(var?i=0;i<classes.length;++i){
????????classNameStr+=classes[i];
????????if(i!=classes[i].length-1){
????????????classNameStr+='?';
????????}
????}
????elem.className=classNameStr;
}

這樣就行，課程中的寫法有什么意義么