How does bool works in javascript

Question

I'm working on that piece of code which doesn't behave as I expected. Especially conditions. In console log I see that objekt.teamA is false, teamA is false, objekt.teamB is true, teamB is true but 1st condition is accepted without any reason.

Could anybody tell me why is that so?

function wsConnect() 
            {
                var objekt = 
                {
                    teamA: document.getElementById('teamA').value,
                    teamB: document.getElementById('teamB').value
                };
                console.log("connect",wsUri);
                ws = new WebSocket(wsUri);
                ws.onmessage = function(msg) 
                {
                    obj = JSON.parse(msg.data);
                    lightsAv = obj.lights;
                    doorsAv = obj.doors;
                    electricAv = obj.electric;
                    teamA = obj.teamA;
                    teamB = obj.teamB;
                    console.log(objekt.teamA + " " + teamA + " " + objekt.teamB + " " + teamB);
                    //objekt.teamA is false, teamA is false, objekt.teamB is true, teamB is true
                    if(objekt.teamA && !teamA)
                    {
                        console.log("1st condition");
                    }
                    if(objekt.teamB && !teamB)
                    {
                        console.log("2nd condition");
                    }
                }
                ws.onopen = function() 
                {
                    document.getElementById('status').innerHTML = "connected";
                    console.log("connected");
                }
                ws.onclose = function() 
                {
                    document.getElementById('status').innerHTML = "not connected";
                    setTimeout(wsConnect,3000);
                }
            }

Thanks a lot.

It's likely that `teamA` and `teamB` are not booleans. Can you show a [mcve] of your HTML as well? — evolutionxbox, Jul 03 '17 at 11:39
Possible duplicate of [How can I convert a string to boolean in JavaScript?](https://stackoverflow.com/questions/263965/how-can-i-convert-a-string-to-boolean-in-javascript) — evolutionxbox, Jul 03 '17 at 11:44
if(objekt.teamA && !teamA) is always equal to true because objekt.teamA is a string and you are comapring a string with boolean true. — abhishek khandait, Jul 03 '17 at 11:44
@abhishekkhandait — No. They are testing the string for truthiness. That's not quote the same. — Quentin, Jul 03 '17 at 11:46

score 4 · Accepted Answer · answered Jul 03 '17 at 11:41

Your claim:

objekt.teamA is false, teamA is false

Your code:

var objekt = 
{
    teamA: document.getElementById('teamA').value,
    teamB: document.getElementById('teamB').value
};

The value of objekt.teamA comes from the value property of a form control. This will always be a string.

So it is not false, it is "false".

Strings of non-zero length are truthy.

if ("false") {
    console.log("a true value")
}

You can test for the value explicitly:

var myVar = "false";

if (myVar !== "false") {
   console.log("It is true");
} else {
   console.log("It is false");
}

score -1 · Answer 2 · answered Jul 03 '17 at 11:46

You are checking if the variable has a truthy value or not. By using,

if( value ) { }

This will evaluate to true if value is not:

null
undefined
NaN
empty string ("")
0
false

To compare boolean value, you can use -

if(varA === false && varB === true){ }

How does bool works in javascript

2 Answers2