末日曙光非天夜翔阅读:asp一小问

function check()
{
if(checkspace(document.searchform.searchkey.value !='请输入关键字')) {
document.searchform.searchkey.focus();
alert("请输入查询关键字！");
return false;
}
if(checkspace(document.searchform.searchkey.value)) {
document.searchform.searchkey.focus();
alert("请输入查询关键字！");
return false;
}
document.searchform.submit();
}
function checkspace(checkstr) {
var str = '';
for(i = 0; i < checkstr.length; i++) {
str = str + ' ';
}
return (str == checkstr);
}
<form name="searchform" method="post" action="research.asp">
<input name="searchkey" type="text" size="16" value="关键字" onFocus="this.value=''">
<input type="submit" name="Submit2" value="立即查询" onClick="return check();" >
<input type="button" name="Submit2" value="高级查询" onClick="location.href='search.asp'">
</form>

请朋友们解释一下上面的检验是怎样执行的,特别是 if(checkspace(document.searchform.searchkey.value !='请输入关键字')) 和if(checkspace(document.searchform.searchkey.value)) 和return (str == checkstr);这三句是什么意思？