How to Add Prefix to a String in Javascript

In this tutorial, you will learn how to add prefix to a string in javascript. A string is made up of many characters. Prefixes are a particular kind of affix that appear at the start of a word and change its meaning. For a newbie developer, it can be a bit tricky to add prefix to a string.

There are numerous ways to add prefix to a string. But for the sake of simplicity, we will make use of addition operator (+) which helps in concatenating two individual strings.

In the following example, we have one global variable that holds a string. Upon click of a button, we will add prefix to a 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 “Add” 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>Add</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 btnAdd and output variables respectively.
  • We have a global variable myString which holds a string as its value.
  • We are displaying myString in the h1 element using innerText property.
  • We have attached a click event listener to the button element.
  • In the event handler function, we have prefix"Keep" stored in the myPrefix variable. We are adding it to the myString using addition operator (+) and storing the final string in the result variable.
  • We are displaying the result in the h1 element using the innerText property.
let btnAdd = document.querySelector("button");
let output = document.querySelector("h1");

let myString = ` it up`;
output.innerText =  myString;
 
btnAdd.addEventListener("click", () => {  
  let myPrefix = "Keep"
  let result = myPrefix + myString;
  output.innerText = result;
});