Where Are The Wise Men?

I spent my morning fixed problems with JavaScript. By “problems” I mean “fixing code that three or four iterations of developers have been too lazy to do correctly.” Here is simplified version of a particularly stupidly-written function that I uncovered:

function addItem(f,addtype) {
if (addtype="ab") {
f.hideme.value='';
functName1();    }
if (addtype="bc") {
f.hideme.value='';
functName2();    } if (addtype="cd") {       f.hideme.value='';           functName3();     }
if (addtype="de") {          f.hideme.value='';      functName4();     }
if (addtype="ef") {
f.hideme.value='';
functName5();     }}

This seems to call for a switch statement, but I’ve never been a fan of switch statements in any language. I understand them, but I’ve found them to be a weird and fragile construct. I instead implemented a function map. That trick works like a charm in Python and I wondered if it worked in JavaScript. And it does — like charm:

function addItem(f,addType) {
f.hideme.value='';
var typeFunctions = {"ab": functName1,
"bc": functName2,
"cd": functName3,
"de": functName4,
"ef": functName5};
if (typeFunctions.hasObjectProperty(addType)) {
typeFunctions[addType]();
}
}

This works because functions in JavaScript are objects like everything else. Note, though, that in my construction of typeFunctions that I didn’t put in a () after each function. That is because I wanted the function object, not the return value of each function. That would have executed each function in the constructor! That was not what I wanted to do. The hasObjectProperty method makes sure that the value in addType is really a property name in typeFunctions. You can also easily more type/function pairs by simply adding them to the typeFunctions constructor.

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This entry was posted on Thursday, May 17th, 2007 at 11:53 am and is filed under javascript. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.