I have a question regarding javascript truthy / falsy
As far as I know, any non-zero number including negative numbers is truthy. But if this is the case then why
-1 == true //returns false
But also
-1 == false //returns false
Can someone shed some light? I would appreciate it.
When using the == operator with a numeric operand and a boolean operand, the boolean operand is first converted to a number, and the result is compared with the numeric operand. That makes your statements the equivalent of:
-1 == Number(true)
and
-1 == Number(false)
Which in turn are
-1 == 1
and
-1 == 0
Which shows why you're always seeing a false result. If you force the conversion to happen to the numeric operand, you get the result you're after:
Boolean(-1) == true //true
No, a boolean is either 0 (false) or 1 (true) like a bit.
Here is an example:
console.log(0 == false); // returns true => 0 is equivalent to false
console.log(1 == true); // returns true => 1 is equivalent to true
console.log(-1 == false); // returns false => -1 is not equivalent to false
console.log(-1 == true); // returns false => -1 is not equivalent to true
Any non-zero number evaluates to true and zero evaluates to false. That is not the same as being equal to true/false.
Executing the code here below (and substituting -1 with different values) could help you understand this:
if (-1) {
true;
} else {
false;
}
In addition to the @James Thorpe answer, if you want to identify zero and non-zero numbers you can use the following code:
console.log(Math.abs(-1) > 0);
console.log(Math.abs(0) > 0);
console.log(Math.abs(1) > 0);