How to change/update CSS class dynamically using amp-bind in Google AMP ?

Last Updated : 25 Oct, 2020

Sometimes you want to add custom interactivity to your AMP pages to make your pages look more user-friendly and user calling. Although AMP’s pre-built components are limited, so amp-bind is made to overcome this problem. It helps the developer to add custom interactivity to the pages without using AMP’s pre-built components. You can use amp-bind to change the text dynamically on user interaction with the page.

Setup: To use amp-bind in your page you have to import its script in the header of the document.

HTML

<script async custom-element="amp-bind"
      src="https://cdn.ampproject.org/v0/amp-bind-0.1.js"> 
</script>

The amp-bind of Google AMP comprises three main concepts:

State: State variables are responsible for the update on the page on the basis of user actions. It is very important to define a state variable.
Expression: They are like JavaScript expressions used to refer to the state.
Binding: They are a special attribute that is used to link an element’s property to a state via an expression.

To change the image’s class we will make use of [class] attribute, it helps to change the class dynamically.

Example:

HTML

<!doctype html> 
<html amp> 
  
<head> 
    <meta charset="utf-8"> 
    <title>Google AMP amp-bind</title> 
  
    <link rel="canonical" href= 
"https://amp.dev/documentation/examples/components/amp-bind/index.html"> 
  
    <meta name="viewport" content= 
"width=device-width,minimum-scale=1,initial-scale=1"> 
  
    <script async src= 
        "https://cdn.ampproject.org/v0.js"> 
    </script> 
  
    <script async custom-element="amp-bind" 
src="https://cdn.ampproject.org/v0/amp-bind-0.1.js"> 
    </script> 
  
    <style amp-boilerplate> 
        body { 
            -webkit-animation: -amp-start 8s  
                steps(1, end) 0s 1 normal both; 
              
            -moz-animation: -amp-start 8s  
                steps(1, end) 0s 1 normal both; 
              
            -ms-animation: -amp-start 8s  
                steps(1, end) 0s 1 normal both; 
              
            animation: -amp-start 8s  
                steps(1, end) 0s 1 normal both; 
        } 
  
        @-webkit-keyframes -amp-start { 
            from { 
                visibility: hidden 
            } 
  
            to { 
                visibility: visible 
            } 
        } 
  
        @-moz-keyframes -amp-start { 
            from { 
                visibility: hidden 
            } 
  
            to { 
                visibility: visible 
            } 
        } 
  
        @-ms-keyframes -amp-start { 
            from { 
                visibility: hidden 
            } 
  
            to { 
                visibility: visible 
            } 
        } 
  
        @-o-keyframes -amp-start { 
            from { 
                visibility: hidden 
            } 
  
            to { 
                visibility: visible 
            } 
        } 
  
        @keyframes -amp-start { 
            from { 
                visibility: hidden 
            } 
  
            to { 
                visibility: visible 
            } 
        } 
    </style> 
    <noscript> 
        <style amp-boilerplate> 
            body { 
                -webkit-animation: none; 
                -moz-animation: none; 
                -ms-animation: none; 
                animation: none 
            } 
        </style> 
    </noscript> 
    <style amp-custom> 
        h1 { 
            color: forestgreen; 
        } 
  
        .gfg { 
            border: 5px solid crimson; 
        } 
    </style> 
</head> 
  
<body> 
    <center> 
        <h1> 
            Geeks For Geeks 
        </h1> 
  
        <div style="padding: 1em;"> 
  
            <amp-img src= 
"https://media.geeksforgeeks.org/wp-content/cdn-uploads/gfg_200x200-min.png"
                width="150"
                height="150" [class]="border"> 
            </amp-img> 
            <br> 
            <button on="tap:AMP.setState({ 
                        border: 'gfg' 
                      })"> 
                Change Class 
            </button> 
        </div> 
    </center> 
</body> 
  
</html>

Output:

Initially, the image has no class but when the button is hit, its class is updated to gfg which has a border attribute thus a border appears on the screen around the image.

Suggest improvement

How to set an image placeholder for amp-anim in Google AMP ?

Google AMP amp-gist

Share your thoughts in the comments