How to use a function that takes arguments with jQuery's change() method?

Question

I'm using jQuery version 1.5. I am looking at jQuery's change() function and specifically at this bit:

.change( [ eventData ], handler(eventObject) ) eventData: A map of data that will be passed to the event handler. handler(eventObject): A function to execute each time the event is triggered. 

What exactly is a "map of data" in JavaScript? How can I use the following test function as an event handler?

var myHandler = function(msg){alert(msg);}; 

I've tried this:

$("select#test").change(["ok"], myHandler); 

and the alert reports [object Object]

Answer 1

See event.data. The data is not passed as argument to handler, but as property of the event object:

$("select#test").change({msg: "ok"},  function(event) {     alert(event.data.msg); }); 

The handler always only accepts one argument, which is the event object. This is the reason why your alert shows "[object Object]", your function is printing the event object.
If you want to use functions with custom arguments, you have to wrap them into another function:

$("select#test").change({msg: "ok"},  function(event) {     myHandler(event.data.msg); }); 

or just

$("select#test").change(function(event) {     myHandler("ok"); }); 

---

Btw. the selector is better written as $('#test'). IDs are (should be) unique. There is no need to prepend the tag name.

Answer 2

What exactly is a "map of data" in Javascript?

Basically just an object, e.g.:

var data = {     foo: "I'm foo",     bar: "I'm bar" }; 

All JavaScript objects are essentially maps (aka "dictionaries" aka "associative arrays").

How can I use the following test function as an event handler?

By wrapping it in another function:

$("select#test").change(function() {     myHandler($(this).val()); }); 

That calls myHandler with the value of the select box whenever it changes.

If you want to use the eventData part, add an object prior to the handler:

$("select#test").change({     foo: "I'm foo" }, function(event) {     myHandler(event.data.foo, $(this).val()); }); 

That calls myHandler with the "I'm foo" as the first argument, then the value of the select box, whenever it changes.