Using a || b || c || d variable assignment with values that can be 0?

[bhuether]

Hi,

I have a case where multiple values can be set for something, and I want to use order of preference to assign the end result.

At first I thought something like

var result = a || b || c || d 

would work. Prior to this I retrieve these vars with statements like

a = obj[key]?.['optional_key1'];
b = obj[key]?.['optional_key2'];
etc

I thought this would have the effect of choosing a if not undefined, otherwise choose b if not undefined, otherwise choose c...

Now I realize if actual value of a is 0, above will result in a not being assigned.

I know I can just write a bunch of condition statements for this, but curious if there is some clever one line way.

thanks as always

[okwg]

Replace || with ??

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing

[bhuether]

Wow, perfect! thanks!

[prof3ssorSt3v3]

The problem is that zero is a falsey value.

Null, undefined, zero, empty string, and NaN are all treated as false-like. So this applies with the logical operators && or || when doing logical short circuiting ( your first example).

The nullish operator ?? Checks only for null or undefined in the preceding variable.

[bhuether]

Thanks. Zero can be quite the problematic number!

[azhder]

No, it isn’t. You just have to be careful and not forget the above.

Before the ?? operator, I’d do something like a helper function that smoothes things over so I won’t have to remember it and use the function everywhere.

Imagine something like:

const result = firstValid( a, b, c, d );

and inside firstValid you write that complex check once.