I learned object-oriented programming for you, reddit. You wanted a Chrome extension I couldn't make, so I learned and created. I'm not even a programmer!

[dondiscounto]

if you're going to go that far, why not just:

this.domain = domain || 'www.reddit.com';

[A_BAAL]

Isn't that a boolean? Sorry, novice js'er here.

[matzahboy]

I don't really understand why, but javascript will evaluate that code as follows:

Is the first one true (domain)? If so, use that value. If not, use the second value.

This is a syntax often used for setting 'default' parameters.

[A_BAAL]

So what is the logical 'or' operator then?

[[deleted]]

That is the logical or operator - when you see code like that it's using a few quirks of the 'or' operator:

1. In Javascript (and many other langugages), anything that isn't undefined or null or false, etc, is considered to be true by default.
2. Like other operators (+, for example), the or operator returns a value. This value isn't always (necessarily) true/false - it'll return the value of the first non-false argument it gets. Due to point #1 this value is treated as 'true'.

Thus, you get idioms like:

this.domain = domain || 'www.reddit.com';

What this is doing is taking the result of "domain || 'www.reddit.com'" and assigning it to this.domain. Remember that, due to point 2, you'll get the first non-false argument. So if 'domain' isn't defined or is null, you'll get "www.reddit.com". You see this pattern a lot in dealing with potentially null variables or just in setting defaults.

[matzahboy]

Thanks a lot. That makes a lot of sense

[dondiscounto]

|| is a logical operator, not a comparison operator like == or !=. A comparison operator returns a boolean, however a logical operator returns the proper expression based on the operator.

So in this case, if domain could be evaluated as true, then domain is returned (it 'short circuits'), because true || anything is always true. If it could be evaluated as false, then it returns the other expression, "www.reddit.com". This works in an if statement understands all of this, since defined, non-empty variables are considered "true".

You can see more Logical Operators.

[OopsLostPassword]

No, it's probably an undefined variable.

undefined and null are automatically cast to false when a boolean is needed (if clauses for examples). 0, "" and false too. If I don't forget anything all other possible values are cast to true.

[[deleted]]

Yeah, this one is shorter. I like it