First Digit must be 0 using JQuery

In this tutorial we will see how to make sure that First Digit must be 0 using JQuery. The indexOf() method is used with JQuery on() method for this purpose.

HTML Code

HTML Code is given below, This code contains an input element inside the form tag.

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>First Digit must be 0 using JQuery</title>
</head>
<script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>    
<body>
 <form>
  <input type="text" id='number'>   
 </form>
</body>
</html>

JQuery Code

JQuery Code is given below, In this code the JQuery on() method is used with indexOf() method.

JQuery on() method

The JQuery on() method is used to attach the event handler with the function for selected elements. In this example it is used to make sure that whenever user inputs a number it triggers a function.

The function then checks that if the entered number is 0 or not.

indexOf() method

The indexOf() method is used to check the position of the first occurrence of a specified value in a variable or a string.

In this code the indexOf() method checks that if the first digit is 0 or not.

Take a look at the code given below.

<script>
$(document).on('input',function(){
  var num=$('#number').val();
  if(num.indexOf('0')!==0){
  alert('First number must be 0');
  $('#number').val('');
  }
});
</script>

Video Tutorial

Watch video tutorial on how to make sure that First Digit must be 0 using JQuery.

Check If Input Field is Empty in jQuery jQuery Select All HTML Elements Whose ID Start With Same String Count Checked Checkboxes of Specific Form with JQuery Enable and Disable Button using JQuery Add Class to HTML Tag On Click Using Jquery Change Class of HTML Tag Using JQuery Display Current Date and Time Using HTML and JQUERY Detect Change in Text Input using JQuery Refresh a Page With JQuery Execute a Function on Hover Using JQuery Open Select File Dialog Box Using JQuery Display Message When File Is Selected Using JQuery Get Class of Clicked Element Using JQuery Remove White Spaces from Start and End of String using JQuery First Digit must be 0 using JQuery OnClick Close and Open Effect using JQuery Display clicked HTML Tag Name using JQuery Delay a Function Execution using JQuery Get ID of Clicked Element using JQuery Change HTML Button Text using JQuery