T.J. Crowder wrote:
> Hi Bill,
>
> If I'm reading you right, you want to pass a callback into another
> function. Functions are first-class objects in JavaScript so there's
> nothing special you need to do (and certainly no need for eval).
>
> Say you have a logging function:
>
> function logMsg(msg) {
> alert(msg); // Obviously not realistic
> }
>
> That function is just an object with a name ("logMsg"). The name is
> valid throughout its containing scope. (If the declaration above is at
> page level, its containing scope is the page; if it's within another
> function, its containing scope is that function.)
>
> Now suppose you want to pass that logging function into another
> function to be used for logging messages. The other function might
> look like this:
>
> function doSomething(logger) {
> logger("This is message one.");
> logger("This is message two.");
> // ...
> }
>
> To do that, just pass it into the function using its name (no quotes):
>
> doSomething(logMsg);
>
> Note that we're just *referring* to the `logMsg` function, not calling
> it. You don't want to do this:
>
> doSomething(logMsg()); // <= WRONG
>
> ...because (as you know) that would _call_ `logMsg` and then pass its
> return value into `doSomething`.
>
> The concept of functions as proper objects is very powerful. We can
> pass functions into other functions (as above). We can assign
> functions to variables:
>
> var f = logMsg;
> f("Log this message");
>
> We can attach functions to objects as properties:
>
> var x = {}; // Create an empty object
> x.logger = logMsg; // Create a property `logger` referencing our
> function
> x.logger("Foo"); // Use it to log "Foo"
>
> You'll recognise some of this from the Prototype API. For instance,
> Enumerable#each accepts a function as a parameter and calls it for
> each item in the enumerable. As Alex mentioned, the Ajax stuff accepts
> an options object that has properties with certain defined names
> ("onSuccess", "onComplete"); the Ajax stuff expects the values of
> those properties to be a function to call.
>
> When passing functions around, there's something you have to remember:
> The *context* (the `this` value) within a function call is set by how
> you *call* the function, not (as it is in several other languages) by
> how/where you define the function. If `this` is going to be
> significant in terms of your callback, I'd suggest reading these posts
> [1] from my (pathetic little) blog.
>
> [1] http://blog.niftysnippets.org/2008/03/mythical-methods.html
> [2] http://blog.niftysnippets.org/2008/04/you-must-remember-this.html
>
> HTH,
> --
> T.J. Crowder
> Independent Software Consultant
> tj / crowder software / com
> www.crowdersoftware.com
>
>
As an advanced javascript neophyte i very much appreciate the extended
reply and the references. It will take me a few days/weeks to digest
and play with this.
Thank you very much.
bill
--
Bill Drescher
william {at} TechServSys {dot} com
--
You received this message because you are subscribed to the Google Groups
"Prototype & script.aculo.us" group.
To post to this group, send email to prototype-scriptacul...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/prototype-scriptaculous?hl=.
