What does this bit of code mean?

Question

Possible Duplicate:
Javascript Shorthand - What Does the '||' Operator Mean When Used in an Assignment?

var variable = obj1 || obj2;

Does it mean this?

var variable;

if (obj1)
{
    variable = obj1;
}
else if (obj2)
{
    variable = obj2:
}

Is it considered bad practise?

possible duplicate of [Javascript Shorthand - What Does the '||' Operator Mean When Used in an Assignment?](http://stackoverflow.com/questions/4511301/javascript-shorthand-what-does-the-operator-mean-when-used-in-an-assignme) and [JavaScript || operator](http://stackoverflow.com/questions/1378619/javascript-operator). — Andy E, Feb 23 '12 at 17:06

score 5 · Accepted Answer · answered Feb 23 '12 at 17:06

The || operator returns its left hand side if resolves to be a true value, otherwise it returns its right hand side.

So it means the same as:

var variable;
if (obj1){
    variable = obj1;
} else {
    variable = obj2:
}

Note else, not, else if.

It is a common pattern and not usually considered bad practise.

The gotcha is that you need to be sure you want if (obj) and not if (typeof obj !== "undefined").

score 0 · Answer 2 · answered Feb 23 '12 at 17:06

0

Yup, that's what it means, and it's good practice

|| is a logical OR, so if obj1 = false you get false OR obj2 so the variable equals obj2

answered Feb 23 '12 at 17:06

JKirchartz

score 0 · Answer 3 · answered Feb 23 '12 at 17:10

How || expression works

The expression a || b value is determined by the last partial evaluated to determine Boolean truth.

false || 1 is evaluated as 1 is the last one evaluated.

true || 0 is evaluated as true as it is the last one evaluated.

For an object in the context of Boolean value, object is evaluated to true unless null. It means even {} === true.

Combine the above two explanation, var variable = obj1 || obj2 assigns the first none null object from obj1 and obj2 to variable.