Why does this if statement succeed with a non-boolean value?

Question

var m = 5;
if (m) {
    document.write(m);
}

In my view, m is not a bool type, therefore, this if statement will not be executed. However, I do see the value of m printed on my screen. Why?

The value doesn't need to be a boolean. The conditional evaluates the value as either truthy or falsy. — Carl Edwards, Jan 10 '20 at 01:55

score 2 · Accepted Answer · answered Jan 10 '20 at 01:55

2

You should read about truthy values (MDN).

In JavaScript, a truthy value is a value that is considered true when encountered in a Boolean context. All values are truthy unless they are defined as falsy (i.e., except for false, 0, 0n, "", null, undefined, and NaN).

Any number other than 0 is truthy, so if(5) is the same as if(true).

answered Jan 10 '20 at 01:55

Ismael Padilla

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Then there's the browser-specific falsy value, `document.all`, which is falsy despite being an object. That's for historical reasons... :-) – T.J. Crowder Dec 05 '21 at 09:37

Why does this if statement succeed with a non-boolean value?

1 Answers1