Check if Javascript boolean is set?

Question

What is the best way to determine if a Javascript boolean is set? Here's an example of what I've been doing. It seems a bit excessive but I need to determine if a value is actually set, not just if it's true:

function doSomething (params, defaults) {

    params = params || {};
    defaults = defaults || {};

    var required = (params.required === true || params.required === false) 
        ? params.required
        : (defaults.required === true || defaults.required === false)
            ? defaults.required
            : true;

    if (required) {
        // perform logic
    }
}

[undefined](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/undefined) would be a good guess. — dokgu, Dec 22 '16 at 19:39
Are you in `use strict` mode or just plain old javascript? :) — Icepickle, Dec 22 '16 at 19:40

score 2 · Answer 1 · answered Dec 22 '16 at 19:40

If a value hasn't been set that means it's undefined.

function printStuff(params) {
  if (params.hello !== undefined) {
    console.log(params.hello);
  } else {
    console.log('Hello, ');
  }
}

printStuff({ });
printStuff({
  hello: 'World'
});

To further drive the point home, here's how it can be used with booleans.

function schrodinger(params) {
  if (params.dead === undefined) {
    console.log('The cat is neither dead nor alive');
  } else if (params.dead) {
    console.log('The cat is dead');
  } else if (!params.dead) {
    console.log('The cat is alive');
  }
}

schrodinger({
  // Not specified
});

schrodinger({
  dead: true
});

schrodinger({
  dead: false
});

score 2 · Answer 2 · answered Dec 22 '16 at 19:40

If you want to check whether an object has a specific property, that's the in keyword:

'required' in params

There's also the hasOwnProperty method, if you need to exclude properties inherited from a prototype (you probably don't for this case):

params.hasOwnProperty('required')

score 0 · Answer 3 · answered Dec 22 '16 at 19:40

0

Would this solve your problem?

if(required!=undefined)

answered Dec 22 '16 at 19:40

nrylee

96
7

Check if Javascript boolean is set?

3 Answers3