Question
What is a good way of assigning a default value to an optional parameter?
Background
I'm playing around with optional parameters in JavaScript, and the idea of assigning a default value if a parameter is not specified. My method in question accepts two parameters, the latter of which I deem to be optional, and if unspecified should default to false. My method looks something like this...
// selects the item, appropriately updating any siblings
// item to select [, toggle on / off]
this.selectItem = function(item, toggle)
{
toggle = toggle && typeof toggle === 'boolean';
if (toggle)
{
// ...
}
}
Testing
After running a few tests on this jsFiddle, using the following principal for default value assigning:
function checkParamIsBoolean(param)
{
param = param && typeof param === 'boolean';
}
checkParamIsBoolean('me'); // boolean
checkParamIsBoolean([]); // boolean
checkParamIsBoolean(true); // boolean
checkParamIsBoolean(false); // boolean
checkParamIsBoolean(1 == 1); // boolean
checkParamIsBoolean(1); // boolean
checkParamIsBoolean(null); // object
checkParamIsBoolean(undefined); // undefined
As you can, the results vary, and aren't desired.
Expected
null = false
undefined = false
Actual
null = object
undefined = undefined
Summary
Are there any alternative approaches to assigning a default value to an optional parameter if it's unspecified; would it be better to use _toggle as the parameter and then assign the value to var toggle within the method?
