How to add readonly attribute to an input tag in JavaScript ?

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Use setAttribute() Method to add the readonly attribute to the form input field using JavaScript.

setAttribute() Method: This method adds the defined attribute to an element, and gives it the defined value. If the specified attribute already present, then the value is being set or changed.

Syntax:

element.setAttribute( attributeName, attributeValue )

Parameters:

attributeName: It is required parameter. It specifies the name of the attribute to be added.
attributeValue: It is required parameter. It specifies the value of the attribute to be added.

Example 1: In this example the read-only attribute of form input text field is enabled by accessing the property.

<!DOCTYPE HTML>  
<html>  
    <head>  
        <title>  
            Add a readonly attribute to an input tag 
        </title> 
    </head>  
  
    <body style = "text-align:center;">  
          
        <h1 style = "color:green;" >  
            GeeksForGeeks  
        </h1> 
          
        <p style = "font-size: 15px; font-weight: bold;"> 
            The readonly attribute is added to input 
            box on click on the button. 
        </p> 
          
        <form> 
            Input : <input id = "Input" type="text"
                name="input_field" /> 
        </form> 
        <br> 
          
        <button onclick = "GFG_Run()"> 
            click here 
        </button> 
          
        <p id = "GFG_down" style =  
            "color: green; font-size: 20px; font-weight: bold;"> 
        </p> 
          
        <script> 
            function GFG_Run() { 
                document.getElementById('Input').readOnly 
                        = true; 
                  
                document.getElementById("GFG_down").innerHTML 
                        = "Read-Only attribute enabled"; 
            } 
        </script>  
    </body>  
</html>                     

Output:

Before click on the button:
After click on the button:

Example 2: In this example the read-only attribute of form input text field is enabled by using setAttribute() method .

<!DOCTYPE HTML>  
<html>  
    <head>  
        <title> 
            Add a readonly attribute to an input tag 
        </title> 
    </head>  
  
    <body style = "text-align:center;">  
          
        <h1 style = "color:green;" >  
            GeeksForGeeks  
        </h1> 
          
        <p style = "font-size: 15px; font-weight: bold;"> 
            The readonly attribute is added to input box 
            on click on the button. 
        </p> 
          
        <form> 
            Input : <input id = "Input" type="text"
                    name="input_field" /> 
        </form> 
        <br> 
          
        <button onclick = "GFG_Run()"> 
            click here 
        </button> 
          
        <p id = "GFG_down" style =  
            "color: green; font-size: 20px; font-weight: bold;"> 
        </p> 
          
        <script> 
            function GFG_Run() { 
                document.getElementById('Input').setAttribute('readonly', true); 
                  
                document.getElementById("GFG_down").innerHTML 
                        = "Read-Only attribute enabled"; 
            } 
        </script>  
    </body>  
</html>                     