js阻止事件默认行为

<script>
window.onload=function(){
document.getElementById('tj').onclick=function(event){
if(document.getElementById('name').value==''){

             window.event.returnValue=false;  //IE

event.preventDefault();  //W3C
}
};
}
</script>
<form >
<input type="text" name="name" id="name">
<input type="submit" value="提交" id='tj'>
</form>