JQuery.proxy is your friend

I'm a Javascript/JQuery newbie and one of the first puzzles that I ran into is callback functions and the value of "this".

You set up a callback handler like so:


jQuery.getJSON('/address/list', this.myCallback);


And you expect that when your callback is invoked that "this" will be set to the value of the enclosing object:


myCallback: function(json) {
    this.doSomething(); // doesnt work!},
doSomething: function() // ...




What you (not so quickly) discover is that JQuery sets the value of "this" to the DOM object (or the element within the DOM that triggered the callback).  It is *not* set to the object that holds your callback function!

The solution is to use JQuery's proxy wrapper:


jQuery.getJSON('/address/list', JQuery.proxy(this.myCallback,this));


You will want to read  this and this for a full explanation.

BTW - none of these results floated to the top of the Google machine. If you are newbie, you probably don't know that you need JQuery.proxy :-).  Hopefully this will help





Comments

Post a Comment

Popular posts from this blog

OAM R2 REST APIs for Policy Management

Image
Oracle Access Manager 11g R2 provides several new REST APIs. This continues a trend to expose key functionality via Web Services. The OAM Mobile and Social service provides APIs for Authentication, Authorization  and User Profile services.  I will cover those APIs in a future article (have a look here for examples) - but today I want to focus on the  policy management APIs. The Policy Administration API  enables to you to interact with OAM to create a variety of Policy objects such as Application Domains, Resources, AuthN Schemes, and AuthN/AuthZ policies. The policy model is shown below: For example, if you want to retrieve all of the resources in an Application Domain you can perform a GET against the /resource URI: curl -u USER:PASSWORD http://<SERVER>:<PORT>/oam/services/rest/11.1.2.0.0/ssa/policyadmin/resource?appdomain="IAM Suite" Note: The port above is where the OAM Admin Server is deployed (often 7001). It ...
Read more

Stupid Oracle vktm tricks to improve VirtualBox performance

In the process of creating a demo VirtualBox image running OEL 6 and the Oracle database 11.2.0.3.0 I noticed the idle CPU consumption was quite high (8% on the guest, 35% on the host). The culprit turned out to be the Oracle database vktm process. This is a time keeping process - and it calls gettimeofday() *very* frequently.  This can have a negative performance impact in virtualized environments. A colleague who is a database whiz suggested the following trick: sqlplus / as sysdba alter system set "_high_priority_processes"='LMS*' scope=spfile;  This removes the vktm process from the list of high priority processes. After this change (you need to bounce the database) the idle CPU consumption comes down to 1-2% or so. A nice improvement! It goes without saying that this is: a) Totally unsupported b) Probably dangerous. This will most certainly break things in the database - such as statistics, auditing, etc. c) For demo/development use...
Read more

Creating an internal CA and signed server certificates for OpenDJ using cfssl, keytool and openssl

Yes, that title is quite a mouthful, and mostly intended to get the Google juice if I need to find this entry again. I spent a couple of hours figuring out the magical incantations, so thought I would document this here. The problem: You want OpenDJ to use something other than the default self-signed certificate for SSL connections.   A "real" certificate signed by a CA (Certificate Authority) is expensive and a pain to procure and install. The next best alternative is to create your own "internal" CA, and  have that CA sign certificates for your services.   In most cases, this is going to work fine for *internal* services that do not need to be trusted by a browser. You might ask why is this better than just using self-signed certificates?  The idea is that you can import your CA certificate once into the truststore for your various clients, and thereafter those clients will trust any certificate presented that is signed by your CA. For example, assu...
Read more