Check that array does not contain falsy values in Jest

Question

I am trying to create a unit test with Jest to make sure my array called values does not contain falsy values.

This for some reason does not work - the test passes:

const badValues = ['', null, undefined, false, {}, []];
expect(values).toEqual(expect.not.arrayContaining(badValues));

Below code works as expected (test fails), but surely there must be a proper way instead of looping over my values?

for (const value of values) {
  expect(value).toBeTruthy();
}

@Pointy You are half right. {} is not falsy, while [] is actually falsy. Try [] == false in your browser. — user6269864
– user6269864, Commented Aug 25, 2018 at 15:40
Try [] ? alert("truthy") : alert("falsy") in your browser. — Pointy
– Pointy, Commented Aug 25, 2018 at 16:07
[] is an empty array, and a reference to any object is always truthy. The == operator is not a good way to test that. — Pointy
– Pointy, Commented Aug 25, 2018 at 16:08

Emeeus · Accepted Answer · 2018-08-25 19:29:49Z

4

It is possible iterating over badValues and then includes() if values and badValues are both arrays of strings or numbers, not objects.

const badValues = ['', 'null', 'undefined', 'false', '{}', '[]'];

var values = [1,2,3,4,'null',5];


for(let i = 0; i<badValues.length; i++){

   if(values.includes(badValues[i])){
       console.log("bad value present");
       break;
   }

}

Otherwise, I think there is no better way than iterating over values. It could be possible using test() and regex, but [,],{,} are all special characters in regex expressions. So we should escape them.

edited Aug 25, 2018 at 19:29

answered Aug 25, 2018 at 13:47

Emeeus

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2 Comments

Jan Ciołek Over a year ago

Comparing objects and arrays like that does not make any sense becase comparison like [] === [] or {} === {} alyways return false..includes wont work with them.

Emeeus Over a year ago

@JanCiolek Yes, that is true, I guessed op had strings. In your case there is no way iterating badvalues.

Maxim Hrustalev · Accepted Answer · 2018-08-27 05:08:01Z

0

May be this can work:

var isValid = arrayOfValuesToBeChecked.reduce(function(prev, elem) {
    // If elem is not truthy and if it is object, check its length 
    elem = elem ? typeof(elem) == 'object' ? elem instanceof Array ? elem.length : Object.keys(elem).length : elem : elem;
    return prev && elem;
}, true);

edited Aug 27, 2018 at 5:08

answered Aug 26, 2018 at 21:38

Maxim Hrustalev

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