If (value === true) not working

Question

Can someone please explain to me why this is not working? The value is true, it is boolean and if I check it like I usually do if(value) {}; it works. Why not like this?

function updateRecords(value) {

  console.log(!!(value));        // true
  console.log(typeof(!!(value)));    //boolean

    if (value === true) {
        alert("success");
      }
 }

    updateRecords("Take a Chance on Me");

It is not a boolean. The "thing" you were running `typeof` against *was* a boolean, due to type casting. To prove it, try logging "typeof(value)" — wally, Dec 24 '16 at 18:32

Scott Marcus · Accepted Answer · 2018-11-04T17:41:12.660

The value that you are working with is a string, not a Boolean. When you wrote this:

console.log(!!(value));

You were converting the string value to a Boolean, but you weren't capturing it. You converted it and logged it and then it got thrown away. Then your next line:

console.log(typeof(value));  // string NOT Boolean

went back to testing the original value of value (a string).

The triple equal sign checks for "type and value equality", so your if test fails.

Now, if you remove one of the equal signs (==) and test for simple "value equality with type conversion", it still won't work unless the text you are testing against converts to the same number that true will (see link below for details), but that won't happen, your string will convert to NaN (not a number) and true will convert to 1, so even value == true will fail.

You can see more details about how equality and type conversion work together here.

At any rate, in this case don't test against the Boolean true, just test for the existence of data: if(value) which doesn't attempt to convert your value to a number, it attempts to convert it to a Boolean. As long as you don't have a string that contains "falsy" values (ie. "", "0", "false", " "), it will convert to true

function updateRecords(value) {

  console.log(!!value);        // true
  console.log(typeof value);    // string

    // Don't test against true (that's implied), just test the data.
    if (value) {
        alert("success");
    }
 }

updateRecords("Take a Chance on Me");

Or, capture the casted version of your data and then you can use ===

function updateRecords(value) {
  // Convert the value of "value" to a Boolean and
  // store that value back in the original variable
  value = !!value;

  // Now, let's test value AFTER capturing its converted value
  console.log(value);            // true
  console.log(typeof value);    // boolean

    if (value === true) {
        alert("success");
      }
 }

updateRecords("Take a Chance on Me");

I thought about comparing it with double equals bit it still didn't work. Can you explain why is that? I was under impression that since !!("Take a Chance on me") is true and the string is truthy that it will wotk if I compare it with boolean value. — Igor-Vuk, Dec 24 '16 at 18:42
@Igor-Vuk Yes, the last thing works. As I said it in my answer, you are not changing the value but you are comparing it with `===`. — Praveen Kumar Purushothaman, Dec 24 '16 at 18:43
@Igor-Vuk It doesn't work with `==` because the values are first converted to numbers, not Booleans and then compared. — Scott Marcus, Dec 26 '16 at 19:38

score 2 · Answer 2 · answered Dec 24 '16 at 18:30

Because you are not yet typecasting in the second instance.

if (!!(value) === true) {
    alert("success");
}

Previously you were checking:

"Take a Chance on Me" === true      // This obviously returns false.

The above should work. Else you shouldn't use the === operator. You should use ==:

if (value == true) {
    alert("success");
}

score 0 · Answer 3 · answered Dec 24 '16 at 19:27

0

JS can be surprising (@praveenkumar alias flashgordon : not always obvious) :

""   == false is true
"1"  == false is false (ok so far)
"0"  == false is true  (looks weird)
" "  == false is true  (wtf...)
"\n" == false is true  (wtf²)

answered Dec 24 '16 at 19:27

That's good information, but a not very good answer to the question. – Scott Marcus Dec 24 '16 at 20:11

If (value === true) not working

3 Answers3