What does this mean: if( variable ){ /* do something */ }

Question

My question is as title says;

What does this mean:

if( variable ){ /* do something */  }

I mean if variable exist do something or what?

Answer 1

It means if variable is truthy , then execute the block. In JavaScript, the following are falsey

• false
• 0
• NaN
• undefined
• null
• "" (Empty String)

Other than the above, everything else is truthy , that is, they evaluate to true .

If the variable didn't exist at all (that is, it had never been declared), that could would throw a ReferenceError because it's trying to read the value of a variable that doesn't exist.

So this would throw an error:

if (variableThatDoesntExist) {
    console.log("truthy");
}

This would log the word "truthy":

var variable = "Hi there";
if (variable) {
    console.log("truthy");
}

And this wouldn't log anything:

var variable = "";
if (variable) {
    console.log("truthy");
}

Answer 2

It's Javacript syntax to check if the variable is truthy or falsy .

It's similar to saying if (variable is true) { /* Do something */}

In Javascript, these are falsy values.

1. false
2. 0 (zero)
3. "" (empty string)
4. null
5. undefined
6. NaN (Not-a-Number)

All other values are truthy, including "0" (zero as string), "false" (false as a string), empty functions, empty arrays, and empty objects.