Which validation method is better?

Question

Is it better to validate user input using this method

if (obj == null) {
   // detects null and undefined
   // exit the function, input not validated
}

or this method

if (!obj) {
    // detects false, 0, -0, '', null, undefined, NaN
    // exit the function, input not validated
}

In this particular case, obj represents an array to be looped through.

I'm having difficulty deciding which method to use.

It all depends on your use case and preference. If you need to be strict, `Array.isArray()` would be a good choice. Else it is up to your preference. — Fabrício Matté, Jul 22 '13 at 22:18
@AndyRay It's not strict equality (`===`) in either case. The OP also acknowledges that the conditionals match different values (which also makes this more of a subjective question ..) — user2246674, Jul 22 '13 at 22:20
you can loop through an empty string. It has a length property. arrays are truthy and empty arrays will fail both tests. google. close. — Andy Ray, Jul 22 '13 at 22:21
@stack_temp: How can it "user input" and "an array"? I've only seen users input strings somewhere, so what do you mean by "represent" (have you parsed it already)? — Bergi, Jul 22 '13 at 22:24
Neither is __better__; you need to validate that the object conforms to whatever rules you've set for it. — Evan Davis, Jul 22 '13 at 22:25
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/33936/discussion-between-mathletics-and-stack-temp) — Evan Davis, Jul 22 '13 at 22:28
`obj == null` will filter out all objects which can not be looped through. — employee-0, Sep 25 '13 at 13:03
it detects null and undefined which are the only object instances that are guaranteed not to have properties...try reading a book. — employee-0, Sep 25 '13 at 13:06

score 1 · Answer 1 · answered Jul 22 '13 at 22:18

1

You've described the differences. So it's up to you - do you want false or '' to pass your conditional or not?

For an array, you may want to consider:

if (obj && obj.length) {
    // Your array is not null, and has items.
}

answered Jul 22 '13 at 22:18

Joe Enos

39,478
11
80
136

@stack_temp If you're worried that `length` might give you a non-number, sure. If you go this route, and still want to validate that it's not an empty array, you'd have to go a step further with `(obj && obj.length && obj.length === +obj.length)`. You could take it another step further and ensure that the type is an array. Personally, I'd stick with simplicity - knowing that the length is "truthy" would be good enough for me. – Joe Enos Jul 23 '13 at 00:54

score 1 · Accepted Answer · answered Jul 22 '13 at 22:22

1

to be honest, since javascript is interpreted anyway, the overhead of the operation is huge compared to actually evaluating it, so it doesn't matter. You can always test by doing it a million times in a loop and timing which is faster.

answered Jul 22 '13 at 22:22

handyprogrammer

56
4

Which validation method is better?

2 Answers2