If you've used knockout.js then you are familiar with the knockout.mapping plugin for creating viewmodels. As awesome as knockout is, the mapping plugin is what made it really practical to use. Unfortunately as I've tried to knockout in business applications I've found the mapping plugin had a few problems:

I presented at JAXDUG tonight on KnockoutJS. Originally I had prepared for an hour timeslot but I got scheduled for a 20 minute Speaker Idol presentation (One night, 5 speakers, 20 minutes each). All in it went really well. It was a ton of content to fit into only 20 minutes. I ran 3 minutes over and flubbed some code, but I think I pulled it off. I'd like to present on it again; I have some ideas on how to do it better.

 I've taken an almost year sabbatical from blogging but I should be back posting regularly now. For the time being I have a lot on my mind about Knockout, MVC and Less.js. The ironic thing is that since I moved from a primarily front end position about six months ago and took a job doing primarily WCF and Web Services I've had a ton of energy in my spare time to dig into fun front end stuff, unburdened by the constraints and limitations of what may be approved for use at work.

Recently I was working with JQuery & Knockout in javascript and got a long running script error so I broke out the profiler to see what was wrong. Unfortunately both JQuery and Knockout code take in a lot of anonymous functions so looking at the profiler and the stack wasn't especially useful. To make the debugger and profiler more more useful I added a name to the function expression that I suspected was causing the problem similar to this:

//Changed form this:
viewModel.FooBar = ko.dependentObservable({
  read: function(){ //Note the anonymous function expression
     return this.foo() && this.bar();
  },
  owner: viewModel
});

//To this:
viewModel.FooBar = ko.dependentObservable({
  read: function readFooBar (){ //Note the name readFooBar 
     return this.foo() && this.bar();
  },
  owner: viewModel
});

These are called named function expressions (NFE's) and they can be seen in both the profiler and the call stack. As it turns out the function that I was troubleshooting didn't have a problem after all. Later the same trick allowed me to verify the real problem was in a custom binding that I had written.

Using named function expressions hasn't been common up till now because there were issues in IE8 and lower, however these issues are easily avoided by 1)giving all named function expressions unique names withing their enclosing scope and 2)NEVER referencing the NFE name in your code (IE9 and other major browsers don't allow you to do this anyway). By following these rules and making this small investment in your code you can earn huge dividends when debugging and profiling.