# JavaScript: How to Check if a Variable Is a String

> Use the typeof operator with strict equality to check if a variable is a string in JavaScript, plus how to test for other built-in types

**URL:** https://sentry.io/answers/check-if-a-variable-is-a-string-in-javascript/

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## The Problem

How can I check whether a variable is a string in JavaScript?

## The Solution

We can do this using JavaScript's [`typeof`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Operators/typeof) operator along with its [strict equality](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Operators/Strict_equality) operator. We can test this with the following code:

```javascript
// Function to test if variable is a string
function isString(variable) {
  return typeof variable === "string";
}

// Variables of different types
let myBool = false;
let myNum = 12;
let myArray = [1, 2, 3]
let myObject = { a: 1, b: 2, c: 3}
let myString = "Hello world!"

// Tests
console.log(isString(myBool)); // will print "false"
console.log(isString(myNum)); // will print "false"
console.log(isString(myArray)); // will print "false"
console.log(isString(myObject)); // will print "false"
console.log(isString(myString)); // will print "true"
```

To check whether a variable is one of JavaScript's other built-in types, we can replace the value on the right-hand side of the `===` with the appropriate string from the Result column of [this table](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Operators/typeof#description). Note that [`null` is considered to be of type `"object"`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Operators/typeof#typeof_null). Additional caveats regarding uninitialized variables and other special cases are detailed in the linked page of the MDN documentation.

To check whether a variable is an instance of a custom-defined class, we must use [`instanceof`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Operators/instanceof) instead.

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*Source: [sentry.io/answers/check-if-a-variable-is-a-string-in-javascript/](https://sentry.io/answers/check-if-a-variable-is-a-string-in-javascript/)*