How to Check if a Variable is False in JavaScript

Check if a Variable is False in JavaScript #

Use the strict equality (===) operator to check if a variable is equal to false - myVar === false. The strict equality operator will return true if the variable is equal to false, otherwise it will return false.

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const a = false;

if (a === false) {
  console.log('✅ a is equal to false');
} else {
  console.log('⛔️ a is not equal to false');
}

We used the strict equality (===) operator to check if a variable stores a false value.

The operator returns a boolean value:

• true if the values are equal
• false if the values are not equal

This means that if we compare false with any other type, the strict equality operator (===) would return false.

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console.log(false === false); // 👉️ true
console.log(false === 'false'); // 👉️ false
console.log(false === 0); // 👉️ false

Here's an example.

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const a = false;

if (!a) {
  console.log(`⛔️️ a is ONE OF
       false, 0, empty string, null, undefined, NaN`);
} else {
  console.log(`🚨 a is NOT
       false, 0, empty string, null, undefined, NaN`);
}

We used the logical NOT (!) operator to flip the value of the variable.

Our if statement checks if the variable is falsy.

The falsy values in JavaScript are: false, 0, "" (empty string), null, undefined, NaN (not a number).

This means that for the if block to run, the variable could be any of the aforementioned 6 falsy values and not necessarily false.

Here is an example of how this could cause issues.

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const a = 0;

if (!a) {
  console.log('✅ this runs');
} else {
  console.log("⛔️ this doesn't run");
}

The if block runs because the variable is set to 0, which is a falsy value.

Instead, it's better to be more explicit.

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const a = 0;

if (a !== 0) {
  console.log("⛔️ this doesn't run");
} else {
  console.log('✅ this runs');
}

Being explicit when comparing values saves yourself and the developers reading your code time.

Further Reading #

• Check if a Variable is equal to True in JavaScript
• Check if a Variable is Not NULL in JavaScript