use javascript button to update fields on case and push through assignment rules

Question

i'm trying to create a javascript button to update some values on a case record and then push it through the assignment rules. the following code updates the fields i want but doesn't push it through the rules, what am i missing??

{!REQUIRESCRIPT("/soap/ajax/31.0/connection.js")} 

var caseObj = new sforce.SObject("Case");
caseObj.RecordTypeId = '01280000000Q9uk';
caseObj.Reason = 'Transfer from Billing';
var result = sforce.connection.update([caseObj]);

assignObj = new sforce.SObject("AssignmentRuleHeader");
assignObj.assignmentRuleId = '01Q80000000Gcdr';
caseObj.Id = '{!Case.Id}';
var result = sforce.connection.update([caseObj]);

if (result[0].success=='false') {
alert(result[0].errors.message);
} else {
location.reload();
}

Answer 1

You forgot to assign the header to the connection:

sforce.connection.AssignmentRuleHeader = { "assignmentRuleId": "01Q80000000Gcdr" };

See this topic for details on how to use headers.

Answer 2

In addition to @sfdcfox answer which is the essence of your problem, curiously, your follow-on issue is that the documentation is in disagreement with the real property name for the alleged AssignmentRuleHeader.

sforce.connection.AssignmentRuleHeader =        // uppercase 'A' does not work
    { "assignmentRuleId": "01Q80000000Gcdr" };  

sforce.connection.assignmentRuleHeader =        // lowercase 'a' does work
    { "assignmentRuleId": "01Q80000000Gcdr" };  

Verified at V37.0 using an Onclick Javascript button.

If you inspect the sforce.connection object prior to setting the headers, you can see the properties all start with a lowercase letter. To say this is confusing given that the doc refers to them in initial Caps is why this community stays in business.