March 15, 2022

How to Check if a Variable is of Type String in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to check if a variable is of type string in javascript. There are certain primitive types in javascript and string is one of them. As the name suggests, any variable that holds a plain text as its value is considered to be of string type.

As you already know, javascript is a weakly typed language so there is no guarantee that the data type of a certain variable going to remain the same through its lifecycle. This makes it more important to learn how you can verify if a variable is of type string before you even start accessing it.

To detect whether a variable is of type string, we can make use of typeof and ternary (?) operators. The typeof operator returns the type of the variable.

In the following example, we have one global variable and upon click of a button, we will check if a variable is of type string and display the result on the screen. Please have a look over the code example and the steps given below.

HTML & CSS

We have 3 elements in the HTML file (div, button, and h1). The div element is just a wrapper for the rest of the elements.
The innerText for the button element is “Check” and for the h1 element, it is “Result”.
We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.
We have also included our javascript file script.js with a script tag at the bottom.

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <link rel="stylesheet" href="style.css">
  <title>Document</title>
</head>

<body>

  <div class="container">    
    <button>Check</button>
    <h1>Result</h1>
  </div>

  <script src="script.js"></script>
</body>

</html>

.container {        
    text-align: center;
}

button {
  margin-top: 10px;
  padding: 10px 20px;
}

Javascript

We have selected the button element and h1 element using the document.querySelector() method and stored them in btnCheck and output variables respectively.
We have attached a click event listener to the button element.
We have a global variable myVariable which holds “Hello World” string as its value.
In the event handler function, we are using typeof and ternary (?) operators to verify whether myVariable is of type string or not. Depending upon the result of the check, we will assign “Yes” or “No” to the result variable.
We are displaying the result in the h1 element using the innerText property.

let btnCheck = document.querySelector("button");
let output = document.querySelector("h1");

let myVariable = "Hello World";

btnCheck.addEventListener("click", () => {
  let result = typeof myVariable === "string" ? "Yes" : "No";
  output.innerText = result;
});

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