不明白怎么回事，请指教

Question

为什么不提示hello world呢？
<form name="ok1">
<input type="text" name="a1"/>
<br><input type="text" name="a2"/>
<br><input type="button" value="ttp"/>
<br><span id="t1"></span>
</form>
<script type="text/javascript">
var a1=document.ok1.a1.value;
var a2=document.ok1.a2.value;
if(a1="")
{
document.write("Hello world");
}
else
{
document.write("H131312ello world");
}
</script>

Answer 1

if(a1=="")

Answer 2

<form name="ok1">
<input type="text" name="a1"/>
<br><input type="text" name="a2"/>
<br><input type="button" value="ttp"/>
<br><span id="t1"></span>
</form>
<script type="text/javascript">
var a1=document.ok1.a1.value;
var a2=document.ok1.a2.value;
if(a1=="")
{
document.write("Hello world");
}
else
{
document.write("H131312ello world");
}
</script>

Answer 3

<p>
&nbsp;</p>
<style type="text/css">
td {  font-size: 9pt}
.title {  font-size: 10.5pt}
.iwhite {
border-left: 1px solid rgb(255,255,255);
  border-right: 1px solid rgb(255,255,255); 
border-top: 1px solid rgb(255,255,255);
border-bottom:1px solid rgb(0.0,255); 
font-family: "Verdana", "Arial", "Helvetica", "sans-serif"; 
font-size: 9pt; color: #298583;background:#ffffff; font-weight: normal}
.igray {font-family: "宋体";
font-size: 9pt;
color: #000000;
background:#ffffff;
font-weight: normal;
border-bottom: 1px solid #D7E0EC;
border-top: 0px solid #DADBE3;
border-right: 0px solid #DADBE3;
border-left: 0px solid #DADBE3;
}
.tabborder {
    border:1px solid #ffffff;
}
.writetd {
    text-align:left;
padding:6px;
}</style>
<SCRIPT type=text/javascript> 
var a1=document.workflowFileinbox.longstr1.value;
var a2=document.workflowFileinbox.longstr2.value;
var a3=document.workflowFileinbox.longstr3.value;
if(a1=="")
{
document.write("审核1没通过");
}
else
{
document.write("审核一通过了");
}
</SCRIPT><p>
<input class="igray" id="4375" name="flash1" /></p><p>
审核1</p>
<p>
&nbsp;<textarea class="igray" cols="60" id="4379" name="审核1" rows="3"></textarea></p>
<p>
审核2</p>
<p>
<textarea class="igray" cols="60" id="4380" name="审核2" rows="3"></textarea></p>
<p>
审核3</p>
<p>
<textarea class="igray" cols="60" id="4381" name="审核3" rows="3"></textarea></p>
<table border="0" cellpadding="0" cellspacing="0" style="border-right-width: 0px; border-top-width: 0px; border-bottom-width: 0px; border-left-width: 0px" width="100%">
<tbody>
<tr>
<td align="middle" height="42" style="border-right-width: 0px; border-top-width: 0px; border-bottom-width: 0px; border-left-width: 0px">
<p>
&nbsp;</p>
<p>
&nbsp;</p>
<p>
&nbsp;</p>
<p>
<font size="+1"><strong>表单名称</strong></font></p>
</td>
</tr>
</tbody>
</table>
<table align="center" border="1" bordercolor="#666666" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="95%">
<tbody>
<tr>
<td align="middle" bgcolor="#ffffff">
文件标题</td>
<td bgcolor="#ffffff" class="writetd" colspan="3">
<input class="igray" name="文件标题" size="40" /><span style="color: #8b4513">（例：生产部张三的串休申请）&nbsp; </span>预算号<input name="文件编号" /></td>
</tr>
<tr valign="center">
<td align="middle" bgcolor="#ffffff" width="16%">
提交部门</td>
<td bgcolor="#ffffff" class="writetd">
<input class="igray" name="拟稿部门" /></td>
<td align="middle" bgcolor="#ffffff">
提交日期</td>
<td bgcolor="#ffffff" class="writetd">
<input class="igray" name="提交日期" /></td>
</tr>
<tr valign="center">
<td align="middle" bgcolor="#ffffff">
提交人</td>
<td bgcolor="#ffffff" class="writetd">
<input class="igray" name="提交人" /></td>
<td align="middle" bgcolor="#ffffff">
&nbsp;办理人</td>
<td bgcolor="#ffffff" class="writetd">
&nbsp;<input class="igray" id="3583" name="办理人" /></td>
</tr>
<tr valign="center">
<td align="middle" bgcolor="#ffffff">
紧急程度</td>
<td bgcolor="#ffffff" class="writetd">
&nbsp;</td>
<td align="middle" bgcolor="#ffffff">
&nbsp;</td>
<td bgcolor="#ffffff" class="writetd">
&nbsp;</td>
</tr>
<tr>
<td align="middle" bgcolor="#ffffff">
&nbsp;123</td>
<td bgcolor="#ffffff" class="writetd" colspan="3">
&nbsp;<input class="igray" id="3997" name="通勤数" /></td>
</tr>
<tr>
<td align="middle" bgcolor="#ffffff">
&nbsp;特明细</td>
<td bgcolor="#ffffff" class="writetd" colspan="3">
&nbsp;<input class="igray" id="4086" name="明细" /></td>
</tr>
</tbody>
</table>
<p>
领导签字：<input class="igray" id="3584" name="经理" /><input class="igray" id="3585" name="总监" /><input class="igray" id="3586" name="副总" /></p>

Answer 4

<form name="workflowFileinbox" action="/oa/modules/workflow/workflowFileinbox.do?method=show&id=96911"
 method="post" encType="multipart/form-data">
<p>
&nbsp;</p>
<style type="text/css">
td {  font-size: 9pt}
.title {  font-size: 10.5pt}
.iwhite {
border-left: 1px solid rgb(255,255,255);
  border-right: 1px solid rgb(255,255,255); 
border-top: 1px solid rgb(255,255,255);
border-bottom:1px solid rgb(0.0,255); 
font-family: "Verdana", "Arial", "Helvetica", "sans-serif"; 
font-size: 9pt; color: #298583;background:#ffffff; font-weight: normal}
.igray {font-family: "宋体";
font-size: 9pt;
color: #000000;
background:#ffffff;
font-weight: normal;
border-bottom: 1px solid #D7E0EC;
border-top: 0px solid #DADBE3;
border-right: 0px solid #DADBE3;
border-left: 0px solid #DADBE3;
}
.tabborder {
    border:1px solid #ffffff;
}
.writetd {
    text-align:left;
padding:6px;
}</style>
<SCRIPT type=text/javascript> 
var a1=document.workflowFileinbox.shenhe1.value;
var a2=document.workflowFileinbox.shenhe2.value;
var a3=document.workflowFileinbox.shenhe3.value;
if(a1=="")
{
document.write("审核1没通过");
}
else
{
document.write("审核一通过了");
}
</SCRIPT><p>
<input class="igray" id="4375" name="flash1" /></p><p>
审核1</p>
<p>
&nbsp;<textarea class="igray" cols="60" id="4379" name="shenhe1" rows="3"></textarea></p>
<p>
审核2</p>
<p>
<textarea class="igray" cols="60" id="4380" name="shenhe2" rows="3"></textarea></p>
<p>
审核3</p>
<p>
<textarea class="igray" cols="60" id="4381" name="shenhe3" rows="3"></textarea></p>
<table border="0" cellpadding="0" cellspacing="0" style="border-right-width: 0px; border-top-width: 0px; border-bottom-width: 0px; border-left-width: 0px" width="100%">
<tbody>
<tr>
<td align="middle" height="42" style="border-right-width: 0px; border-top-width: 0px; border-bottom-width: 0px; border-left-width: 0px">
<p>
&nbsp;</p>
<p>
&nbsp;</p>
<p>
&nbsp;</p>
<p>
<font size="+1"><strong>表单名称</strong></font></p>
</td>
</tr>
</tbody>
</table>
<table align="center" border="1" bordercolor="#666666" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="95%">
<tbody>
<tr>
<td align="middle" bgcolor="#ffffff">
文件标题</td>
<td bgcolor="#ffffff" class="writetd" colspan="3">
<input class="igray" name="文件标题" size="40" /><span style="color: #8b4513">（例：生产部张三的串休申请）&nbsp; </span>预算号<input name="文件编号" /></td>
</tr>
<tr valign="center">
<td align="middle" bgcolor="#ffffff" width="16%">
提交部门</td>
<td bgcolor="#ffffff" class="writetd">
<input class="igray" name="拟稿部门" /></td>
<td align="middle" bgcolor="#ffffff">
提交日期</td>
<td bgcolor="#ffffff" class="writetd">
<input class="igray" name="提交日期" /></td>
</tr>
<tr valign="center">
<td align="middle" bgcolor="#ffffff">
提交人</td>
<td bgcolor="#ffffff" class="writetd">
<input class="igray" name="提交人" /></td>
<td align="middle" bgcolor="#ffffff">
&nbsp;办理人</td>
<td bgcolor="#ffffff" class="writetd">
&nbsp;<input class="igray" id="3583" name="办理人" /></td>
</tr>
<tr valign="center">
<td align="middle" bgcolor="#ffffff">
紧急程度</td>
<td bgcolor="#ffffff" class="writetd">
&nbsp;</td>
<td align="middle" bgcolor="#ffffff">
&nbsp;</td>
<td bgcolor="#ffffff" class="writetd">
&nbsp;</td>
</tr>
<tr>
<td align="middle" bgcolor="#ffffff">
&nbsp;123</td>
<td bgcolor="#ffffff" class="writetd" colspan="3">
&nbsp;<input class="igray" id="3997" name="通勤数" /></td>
</tr>
<tr>
<td align="middle" bgcolor="#ffffff">
&nbsp;特明细</td>
<td bgcolor="#ffffff" class="writetd" colspan="3">
&nbsp;<input class="igray" id="4086" name="明细" /></td>
</tr>
</tbody>
</table>
<p>
领导签字：<input class="igray" id="3584" name="经理" /><input class="igray" id="3585" name="总监" /><input class="igray" id="3586" name="副总" /></p>
</form>