How to Adjust the Width of Input Field Automatically using JavaScript ?

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The HTML <input> element is used to create interactive controls for web-based forms in order to accept data from the user. The <input> element is one of the most powerful and complex in all of HTML due to the sheer number of combinations of input types and attributes. The HTML <input> width attribute is used to specify the width of the element.

To increase the width of <input> element dynamically.
Approach 1:

The onkeypress event occurs when the user presses any key.
Select the width attribute of an element.
Make it equal to the length of the value of the input field by this.value.length

<input type="text" onkeypress="myFunction()">

Here, we select the <input> element and add a method to it which occurs when a key is pressed. This method selects and updates the value of the width property dynamically.

HTML Code:

<!DOCTYPE html>  
<html>  
<head>  
    <title> How to adjust width of  
an input field to its input?</title>  
</head>  
<body>  
    <form method="post" action=""> 
        <label for="username">Input text</label> 
        <input type="text" id="textbox" 
        name="textbox" placeholder="Welcome"
        onkeypress="this.style.width =  
            ((this.value.length + 1) * 8) + 'px';"
        id="input"/> 
    </form> 
</body>  
</html>                  

You can also write a JavaScript function to check the length of your string on input change, then adjust the width of the input based on the number of chars * character width.

Alternative JavaScript Code:

$('input').css('width', (( 
  input.getAttribute('placeholder').length + 1) * 8) + 'px'); 
$("input").focusout(function() { 
    if (this.value.length > 0) { 
        this.style.width =  
          ((this.value.length + 1) * 8) + 'px'; 
    } else { 
        this.style.width =  
          ((this.getAttribute('placeholder').length + 1) * 8) 
        + 'px'; 
    } 
}); 

Output:

Approach 2: Use jQuery keypress() event in combination with String.fromCharCode(e.which) to get the pressed character. Hence, we can calculate the width of the input element.

jQuery Code:

$('input[type="text"]').keypress(function(e) { 
    if (e.which !== 0 && e.charCode !== 0) {  
  
        // Only characters 
        var c = String.fromCharCode(e.keyCode|e.charCode); 
        $span = $(this).siblings('span').first(); 
  
        // The hidden span takes  
        $span.text($(this).val() + c) ;  
  
        // The value of the input 
        $inputSize = $span.width() ;  
  
        // Apply width of the span to the input 
        $(this).css("width", $inputSize) ; 
     } 
}) ; 