Symfony 4 : how to handle back arrow after form submit

Question

I have a form which is generated with a random algorithm (quiz test). After submit the render is a result page: the problem is if the user clicks on the back arrow, the form with the same questions will be displayed and can be submitted again! I tried to set a session variable and play with twig function { if app.sesseion->get('myVaryable') is defined } then don't display the submit button etc... but even when the variable is removed in my controller, twig still consider it as defined? Do you have another simple solution?

Answer 1

Clicking the back button in the browser usually results in a page reloaded from the cache (no interaction with the server) so you can't control this with twig (back-end code) unless the user refreshes the page (re-sends request to server).

You need a javascript (front-end code) solution like below, to check the navigation type.

if (window.performance && window.performance.navigation.type == window.performance.navigation.TYPE_BACK_FORWARD) {

    // Disable the form
    var inputs = document.getElementsByTagName("INPUT");
    for (var i = 0; i < inputs.length; i++) {
        inputs[i].disabled = true;
        if (inputs[i].type === 'submit') {
            inputs[i].remove();   
        }
    }

}

I recommend you also look for, and appropriately handle, duplicate submissions in the controller that handles the form, as any skilled user could still submit the form.

References:

detecting back button click

disabling inputs