如何使用Javascript選擇複選框時需要一個字段？

Question

我有一個簡短的表單，需要一些驗證幫助。目前的JavaScript需要每個字段完成...除了電話號碼。但是，如果有人選擇聯繫進行諮詢，我希望要求電話領域。希望我目前的工作不必被拋棄。任何幫助都會很棒。謝謝！

的Javascript：

<script type="text/javascript"> 

function validateForm(f) 
{ 
    // If they entered an email address, then edit it before submitting the form 

    // Require Email Address 
    if (f. field_45042.value == '') 
    { 
     alert('Please enter your email address.') 
     f. field_45042.focus() 
     return false; 
    } 

    // Require First Name 
    if (f. field_57841.value == '') 
    { 
     alert('Please enter your first name.') 
     f. field_57841.focus() 
     return false; 
    } 

    // Require Last Name 
    if (f. field_57842.value == '') 
    { 
     alert('Please enter your last name.') 
     f. field_57842.focus() 
     return false; 
    } 

    // Require Zip Code 
    if (f. field_70761.value == '') 
    { 
     alert('Please enter your zip code.') 
     f. field_70761.focus() 
     return false; 
    } 

    // Require Location 
    if (f.field_70694[0].selected == true) 
    { 
     alert('Please select a store location.') 
     f.field_70694.focus() 
     return false; 
    } 
} 

// --> 
</script> 

HTML：

Email Address:<input type="text" id="field_45042" class="text_field" size="35" name="45042" value="" /> 
First Name:<input type="text" id="field_57841" class="text_field" size="35" name="45043[57841]" value="" /> 
Last Name:<input type="text" id="field_57842" class="text_field" size="35" name="45044[57842]" value="" /> 
Zip Code:<input type="text" id="field_70761" class="text_field" size="35" name="45045[70761]" value="" /> 
Telephone:<input type="text" id="field_62646" class="text_field" size="35" name="45046[62646]" value="" /> 

Preferred Store Location: 
<select id="field_70694" class="select field" name="42714[70694]" > 
    <option value="Select One of the Following:" >Select one of the following:</option> 
    <option value="Store 1" >Store 1</option> 
    <option value="Store 1" >Store 2</option> 
    <option value="Store 1" >Store 3</option> 
</select> 

Please contact me for a FREE consultation. 
<select id="field_71849" class="select field" name="45924[71849]" > 
    <option value="Yes">Yes</option> 
    <option value="No" >No</option> 
</select> 

Answer 1

這應該工作：

if (f.field_71849.value == "Yes" && f.field_62646.value == '') { 

    alert('Please enter a phone number.') 
    f.field_62646.focus() 
    return false; 
} 

Answer 2

// ... 

// require phone if wants to be contacted 
if(f.field_71849.value == 'Yes' && f.field_62646.value == ''){ 
    alert('Please enter your phone number'); 
    return false; 
} 

// ...