Once a Boolean variable is declared is it automatically true?

Question

I heard from someone that once you declare a Boolean variable and set it equal to a condition, that condition is automatically true, but, what happens if you don't set a condition?

Answer 1

In javascript not declarate variables are "undefined" and that is not the same as "false".
Variable 0, -0, null, false, NaN or empty string is also "undefined" all other is true (false also).

function check (){

var boolean1;
var boolean2 = true;
var boolean3 = false;

if(boolean1){
console.log("boolean1 true");
}
else{
console.log(boolean1);
}

if(boolean2){
console.log("bolean2 true");
}
else{
console.log(boolean2);
}

if(boolean3){
console.log("bolean3 true");
}
else{
console.log(boolean3);
}

}

This code returns:
undefined
boolean2 true
false