| | AJAX with jQuery |
| | ================ |
| |
|
| | `jQuery`_ is a small JavaScript library commonly used to simplify working |
| | with the DOM and JavaScript in general. It is the perfect tool to make |
| | web applications more dynamic by exchanging JSON between server and |
| | client. |
| |
|
| | JSON itself is a very lightweight transport format, very similar to how |
| | Python primitives (numbers, strings, dicts and lists) look like which is |
| | widely supported and very easy to parse. It became popular a few years |
| | ago and quickly replaced XML as transport format in web applications. |
| |
|
| | .. _jQuery: https://jquery.com/ |
| | |
| | Loading jQuery |
| | -------------- |
| | |
| | In order to use jQuery, you have to download it first and place it in the |
| | static folder of your application and then ensure it's loaded. Ideally |
| | you have a layout template that is used for all pages where you just have |
| | to add a script statement to the bottom of your ``<body>`` to load jQuery: |
| | |
| | .. sourcecode:: html |
| | |
| | <script src="{{ url_for('static', filename='jquery.js') }}"></script> |
| | |
| | Another method is using Google's `AJAX Libraries API |
| | <https://developers.google.com/speed/libraries/>`_ to load jQuery: |
| |
|
| | .. sourcecode:: html |
| |
|
| | <script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script> |
| | <script>window.jQuery || document.write('<script src="{{ |
| | url_for('static', filename='jquery.js') }}">\x3C/script>')</script> |
| |
|
| | In this case you have to put jQuery into your static folder as a fallback, but it will |
| | first try to load it directly from Google. This has the advantage that your |
| | website will probably load faster for users if they went to at least one |
| | other website before using the same jQuery version from Google because it |
| | will already be in the browser cache. |
| |
|
| | Where is My Site? |
| | ----------------- |
| |
|
| | Do you know where your application is? If you are developing the answer |
| | is quite simple: it's on localhost port something and directly on the root |
| | of that server. But what if you later decide to move your application to |
| | a different location? For example to ``http://example.com/myapp``? On |
| | the server side this never was a problem because we were using the handy |
| | :func:`~flask.url_for` function that could answer that question for |
| | us, but if we are using jQuery we should not hardcode the path to |
| | the application but make that dynamic, so how can we do that? |
| | |
| | A simple method would be to add a script tag to our page that sets a |
| | global variable to the prefix to the root of the application. Something |
| | like this: |
| | |
| | .. sourcecode:: html+jinja |
| | |
| | <script> |
| | $SCRIPT_ROOT = {{ request.script_root|tojson }}; |
| | </script> |
| | |
| | |
| | JSON View Functions |
| | ------------------- |
| | |
| | Now let's create a server side function that accepts two URL arguments of |
| | numbers which should be added together and then sent back to the |
| | application in a JSON object. This is a really ridiculous example and is |
| | something you usually would do on the client side alone, but a simple |
| | example that shows how you would use jQuery and Flask nonetheless:: |
| |
|
| | from flask import Flask, jsonify, render_template, request |
| | app = Flask(__name__) |
| |
|
| | @app.route('/_add_numbers') |
| | def add_numbers(): |
| | a = request.args.get('a', 0, type=int) |
| | b = request.args.get('b', 0, type=int) |
| | return jsonify(result=a + b) |
| |
|
| | @app.route('/') |
| | def index(): |
| | return render_template('index.html') |
| |
|
| | As you can see I also added an `index` method here that renders a |
| | template. This template will load jQuery as above and have a little form where |
| | we can add two numbers and a link to trigger the function on the server |
| | side. |
| |
|
| | Note that we are using the :meth:`~werkzeug.datastructures.MultiDict.get` method here |
| | which will never fail. If the key is missing a default value (here ``0``) |
| | is returned. Furthermore it can convert values to a specific type (like |
| | in our case `int`). This is especially handy for code that is |
| | triggered by a script (APIs, JavaScript etc.) because you don't need |
| | special error reporting in that case. |
| | |
| | The HTML |
| | -------- |
| | |
| | Your index.html template either has to extend a :file:`layout.html` template with |
| | jQuery loaded and the `$SCRIPT_ROOT` variable set, or do that on the top. |
| | Here's the HTML code needed for our little application (:file:`index.html`). |
| | Notice that we also drop the script directly into the HTML here. It is |
| | usually a better idea to have that in a separate script file: |
| |
|
| | .. sourcecode:: html |
| |
|
| | <script> |
| | $(function() { |
| | $('a#calculate').bind('click', function() { |
| | $.getJSON($SCRIPT_ROOT + '/_add_numbers', { |
| | a: $('input[name="a"]').val(), |
| | b: $('input[name="b"]').val() |
| | }, function(data) { |
| | $("#result").text(data.result); |
| | }); |
| | return false; |
| | }); |
| | }); |
| | </script> |
| | <h1>jQuery Example</h1> |
| | <p><input type=text size=5 name=a> + |
| | <input type=text size=5 name=b> = |
| | <span id=result>?</span> |
| | <p><a href= |
| |
|
| | I won't go into detail here about how jQuery works, just a very quick |
| | explanation of the little bit of code above: |
| | |
| | 1. ``$(function() { ... })`` specifies code that should run once the |
| | browser is done loading the basic parts of the page. |
| | 2. ``$('selector')`` selects an element and lets you operate on it. |
| | 3. ``element.bind('event', func)`` specifies a function that should run |
| | when the user clicked on the element. If that function returns |
| | `false`, the default behavior will not kick in (in this case, navigate |
| | to the `#` URL). |
| | 4. ``$.getJSON(url, data, func)`` sends a ``GET`` request to `url` and will |
| | send the contents of the `data` object as query parameters. Once the |
| | data arrived, it will call the given function with the return value as |
| | argument. Note that we can use the `$SCRIPT_ROOT` variable here that |
| | we set earlier. |
| | |
| | Check out the :gh:`example source <examples/javascript>` for a full |
| | application demonstrating the code on this page, as well as the same |
| | thing using ``XMLHttpRequest`` and ``fetch``. |
| | |
