验证不能为空，null，多个空格的js

function validatename(){

var text=document.getElementById('username').value;

//if(text==null||text==''){

//不为空和输入的不是空格

if(text==null||text.replace(/^\s+,""/).replace(/^\s+$/,"")==''){

alert('用户名不能为空！');

//重新获得焦点

document.getElementById('username').focus();

return false;

}

return true;

}

<script language="javascript">
function ec(){
var ss=" fsd fsdaf";
alert(ss.replace(/[ ]/g,""));
}
ec();
</script>