JavaScript Check if a Variable Is a String

There are two simple ways you can check if a variable is a string in JavaScript:

1. Using the typeof operator
2. Using the instanceof operator

Both are used in different ways, so let’s see a quick example of how to use these.

Using the typeof operator

The typeof operator is used to check the type of a variable. You can add an equality comparison operator === to check if the variable is of ‘string’ type:

let myVariable = 'Hello';

console.log(typeof myVariable === 'string'); // true

The comparison returns true when the variable is indeed a string. You can use an if-else statement to let JavaScript know what to do when the variable is a string or not:

let myVariable = 'Hello';

if (typeof myVariable === 'string') {
  console.log('The variable is a string');
} else {
  console.log('The variable is NOT a string');
}

But keep in mind that this comparison will return false when you have a String object and not a string primitive. Consider the following example:

let myVariable = new String('Hello');

if (typeof myVariable === 'string') {
  console.log('The variable is a string');
} else {
  console.log('The variable is NOT a string'); // ✅
}

This code will trigger the else statement because the String() constructor creates an object type value.

To check for this kind of string, you need to use the instanceof operator.

Using the instanceof operator

The instanceof operator is used to test whether a specific constructor appears or is used to create the object you test with this operator.

Because we’re testing a String object, you can use the operator like this:

let myVariable = new String('Hello');

if (myVariable instanceof String) {
  console.log('The variable is a string'); // ✅
} else {
  console.log('The variable is NOT a string'); 
}

Because the String() constructor is used to create the object, the operator returns true.

But if you test a primitive string value, then the instanceof operator would return false. You need to use the solution appropriate for your case.

And that’s how you check if a variable is a string in JavaScript. Hope that helps and happy coding! 👍