Question

I was looking through some compiled coffee-script code, and I noticed something like the following, which I thought was really strange:

var current, x = 8;
current = this._head || (this._head = x);

after running this, current has a value of 8. Judging by the way that the || logical operator works, I would have expected it to evaluate the left side first. After getting an ‘undefined’ on the left hand side, it moves onto the right, where it assigns this._head to 8. Afterwards it returns a true, but this part isn’t that important? I don’t see how it could go back and affect the “current” variable? Any help would be appreciated, thanks!

Answer 1

The || operator returns the value, not true. Maybe it helps to say that

current = this._head || (this._head = x)

could also be written as

current = this._head ? this._head : (this._head = x);

or

current = this._head;

if(!current)
    current = this._head = x;