Check if a Variable is Not NULL in JavaScript

Check if a Variable is Not NULL in JavaScript #

Use the strict inequality (!==) operator to check if a variable is not null - myVar !== null. The strict inequality operator will return true if the variable is not equal to null and false otherwise.

index.js

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const a = 'hello';

if (a !== null) {
  console.log('✅ a is NOT null');
} else {
  console.log('⛔️ a is null');
}

We used the strict inequality (!==) operator to check if the value stored in the variable a is not equal to null.

The operator returns a boolean result:

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

index.js

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console.log(null !== null); // 👉️ false
console.log('hello' !== null); // 👉️ true

The strict inequality (!==) operator considers two values of different types to be different, as opposed to the loose inequality (!=) operator.

This means that if you compare null with any other type, the strict inequality (!==) operator will always return false.

A very common mistake is to check if a value is truthy, instead of checking if it's null. Here's an example.

index.js

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const a = 'hello';

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

In this example, we check if the value stored in the variable a is truthy. Truthy are all values that are not falsy.

The falsy values in JavaScript are: false, 0, "", null, undefined, NaN.

This means that if the else block runs the value of a is falsy and could be either of the 6 falsy values, not necessarily null.

Things could go wrong in so many different ways when doing this, for example if the value of a is equal to 0, the else block runs.

index.js

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const a = 0;

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

Even if this is what you want, you should never write code like this, because it's confusing and indirect.

Instead you should be more explicit:

index.js

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const a = 0;

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

It's always recommended to explicitly use the strict operators (!==, ===) when making equality comparisons. They make your code more readable, explicit and less prone to errors.

Check if a Variable is Not NULL in JavaScript