window.onload = function(){ var gaga = document.getElementById( "gaga" ); addClass( gaga,"gaga1" ) addClass( gaga,"gaxx" ); removeClass( gaga,"gaga1" ) removeClass( gaga,"gaga" ) function hasClass( elements,cName ){ return !!elements.className.match( new RegExp( "(\\s|^)" + cName + "(\\s|$)") ); // ( \\s|^ ) 判断前面是否有空格 （\\s | $ ）判断后面是否有空格 两个感叹号为转换为布尔值 以方便做判断 }; function addClass( elements,cName ){ if( !hasClass( elements,cName ) ){ elements.className += " " + cName; }; }; function removeClass( elements,cName ){ if( hasClass( elements,cName ) ){ elements.className = elements.className.replace( new RegExp( "(\\s|^)" + cName + "(\\s|$)" )," " ); // replace方法是替换 }; }; };