Troubleshooting (Script Authors): Difference between revisions

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m (→‎Form POST data: Marked as good example)
Line 18: Line 18:
Problem example:
Problem example:


{{Bad example|1=<pre style="border: none; margin: inherit;">for (var i = 0; i < document.links.length; i++) {
{{Bad example |1=<pre style="border: none; margin: inherit;">
for (var i = documents.links.length - 1; i >= 0; --i) {
   var link = document.links[i];
   var link = document.links[i];
    
    
   GM_xmlhttpRequest({
   GM_xmlhttpRequest({
     method:"GET",
     method: "GET",
     url:"&#104;ttp://example.com/lookup?url=" + link.href,
     url: "http://example.com/lookup?url=" + link.href,
     onload:function(result) {
     onload: function(result) {
       link.href = result.responseText;
       link.href = result.responseText;
     }
     }
Line 35: Line 36:


Solution example with named function:
Solution example with named function:
<code><pre>
{{Good example |1=<pre style="border: none; margin: inherit;">
function do_it(link_inside) {
function do_it(link_inside) {
   GM_xmlhttpRequest({
   GM_xmlhttpRequest({
     method:"GET",
     method: "GET",
     url:"&#104;ttp://example.com/lookup?url=" + link_inside.href,
     url: "http://example.com/lookup?url=" + link_inside.href,
     onload:function(result) {
     onload: function(result) {
       link_inside.href = result.responseText;
       link_inside.href = result.responseText;
     }
     }
Line 46: Line 47:
}
}
    
    
for (var i = 0; i < document.links.length; i++) {
for (var i = documents.links.length - 1; i >= 0; --i) {
   var link = document.links[i];
   var link = document.links[i];
    
    
   do_it(link);
   do_it(link);
}
}
</pre></code>
</pre>}}
Solution example with anonymous function:
Solution example with anonymous function:


<code><pre>
{{Good example |1=<pre style="border: none; margin: inherit;">
for (var i = 0; i < document.links.length; i++) {
for (var i = documents.links.length - 1; i >= 0; --i) {
   var link = document.links[i];
   var link = document.links[i];
    
    
Line 61: Line 62:
    
    
     GM_xmlhttpRequest({
     GM_xmlhttpRequest({
       method:"GET",
       method: "GET",
       url:"&#104;ttp://example.com/lookup?url=" + link_inside.href,
       url: "http://example.com/lookup?url=" + link_inside.href,
       onload:function(result) {
       onload: function(result) {
         link_inside.href = result.responseText;
         link_inside.href = result.responseText;
       }
       }
Line 70: Line 71:
   })(link);
   })(link);
}
}
</pre></code>
</pre>}}


== Component not Available errors ==
== Component not Available errors ==

Revision as of 21:17, 6 May 2009

The article Avoid Common Pitfalls in Greasemonkey covers some of the most common problems people come across when writing user scripts.

If your problem is not listed, please ask on the mailing list.

Changes don't take effect when editing a script

You may be editing your original copy of the script, not the installed copy. Once you create and install a script, you need to follow these steps to make sure you're editing the installed, active copy.

Also, changing the include and exclude rules in the metadata block of the installed script does not do anything, as the script metadata is only accessed during installation. The script must be re-installed (or config.xml edited manually) for these changes to take.

Note: You can change the include and exclude rules in the Manage User Scripts window and those changes will take effect.

Variables change before a GM_xmlhttpRequest or setTimeout callback runs

Problem example:

Template:Bad example

The request is asynchronous, meaning the rest of the code doesn't wait for it to complete. The for keeps running as the request loads. When the request for the first link on the page completes and the onload callback function runs, the link variable might point to a different link altogether, typically the last one (since the for loop completes much quicker than the HTTP requests).

One solution is to pass those values that you want unchanged into a function surrounding the request, as arguments. Then they will be in a different scope, and will no longer be changed from the outside.

Solution example with named function: Template:Good example Solution example with anonymous function:

Template:Good example

Component not Available errors

These are usually caused by attempting to access an element's event handlers (onclick, onkeydown, etc.) directly, rather than through addEventListener. GreaseMonkey 0.5 and above require the use of addEventListener. For details, see XPCNativeWrapper.

Form POST data

When using GM_xmlhttpRequest to POST form data, remember to add the Content-Type parameter:

Template:Good example

Links

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