How to Check if a Variable is a String in JavaScript

This quick tip will show you how to check if a variable is a string in the JavaScript Programming Language.

What is a String?

A string is a type of variable. A variable type determines what values a variable can contain and what can be done with the variable.

Strings are a series of characters – letters or numbers or symbols. They can be joined, split, and iterated over.

Strings are used to store words, sentences, and other non-numeric data like encoded images or serialized data which is going to be transmitted.

Checking if a Variable is a String with JavaScript’s typeof

The typeof command in JavaScript returns the type of the object it is called on. It returns a string containing the name of the type.

In this case, we want to check that the type of the variable named testMe is “string” – so a simple comparison can be used:

if (typeof testMe === 'string') {
    // String
}
else {
    // Not a string
}

The === operator is used to ensure that the typeof the given variable is an exact match for “string” – both in value and type.

Checking if a Variable is Not a String

The reverse can also be done by reversing the equality check:

if (typeof testMe !== 'string') {
    // Not a string
}
else {
    // String
}

Why?

There are any number of reasons why you would want to check if a variable is or is not a string based on your use case. For example, you may wish to check that values are not strings before trying to perform arithmetic or boolean logic on them.