Re: 'in' operator and feature detection technique...

Luke Matuszewski wrote:

> if("write" in document) {

> So i have questioned myself what for ? I can always do:
>
> if(document["write"]) {

> I can only guess that 'in' was
> provided in W. IE 5.5 only for convenience...

The in operator checks whether there is a property with the name as the
first operand, that is much different to converting the property value
to a boolean (which if () does).

Example

var testObject = {
   b : false,
   s : '',
   n: 0
};

var results = '';

for (var propertyName in testObject) {
   results += 'Boolean(obj["' + propertyName + '"]): ' +
Boolean(testObject[propertyName]) + '\r\n';
   results += '"' + propertyName + '" in obj: ' +
(propertyName in testObject) + '\r\n\r\n';
}

results

yields

Boolean(obj["b"]): false
"b" in obj: true

Boolean(obj["s"]): false
"s" in obj: true

Boolean(obj["n"]): false
"n" in obj: true

-- 
	Martin Honnen
	http://JavaScript.FAQTs.com/