Dynamic Form Validation in Flask with AJAX and Custom JSON Responses
Building an application that showcases real-time data entry forms in Flask, I've hit a snag with validating user inputs dynamically. The requirement is to validate fields as the user types, using AJAX to send the input to the backend and receive JSON responses for feedback. The forms utilize WTForms for validation, but I need to ensure that each field's validation triggers without a full page refresh. Currently, I've set up a simple Flask route to handle the incoming AJAX requests. Here's the code snippet: ```python from flask import Flask, request, jsonify from wtforms import Form, StringField, validators app = Flask(__name__) class MyForm(Form): username = StringField('Username', [validators.Length(min=4, max=25)]) @app.route('/validate', methods=['POST']) def validate(): form = MyForm(request.form) if form.validate(): return jsonify({'status': 'success', 'message': 'Valid input'}), 200 else: return jsonify({'status': 'error', 'message': str(form.username.errors)}), 400 ``` When I send an AJAX request with the username input, I expect a JSON response indicating whether the input is valid or not. However, even when I provide valid input, I receive an error message stating that the length must be between 4 and 25 characters. Here’s the AJAX call I'm using: ```javascript $('#username').on('input', function() { $.ajax({ type: 'POST', url: '/validate', data: { username: $(this).val() }, success: function(response) { // handle success }, error: function(response) { // handle error } }); }); ``` I've tried different configurations for the form submission, like ensuring the input values are properly sent and that I'm not missing any CSRF tokens, but the error keeps appearing. Is there a subtle issue with how WTForms handles these AJAX calls, or am I overlooking something in the form validation logic? Any insights on debugging this scenario or best practices for implementing dynamic form validation in Flask would be greatly appreciated! I'm using Python LTS in this project. Any ideas how to fix this?