mirror of https://github.com/mitsuhiko/flask.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
166 lines
6.7 KiB
166 lines
6.7 KiB
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: http://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 type=text/javascript src="{{ |
|
url_for('static', filename='jquery.js') }}"></script> |
|
|
|
Another method is using Google's `AJAX Libraries API |
|
<https://developers.google.com/speed/libraries/devguide>`_ 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 type=text/javascript> |
|
$SCRIPT_ROOT = {{ request.script_root|tojson|safe }}; |
|
</script> |
|
|
|
The ``|safe`` is necessary in Flask before 0.10 so that Jinja does not |
|
escape the JSON encoded string with HTML rules. Usually this would be |
|
necessary, but we are inside a ``script`` block here where different rules |
|
apply. |
|
|
|
.. admonition:: Information for Pros |
|
|
|
In HTML the ``script`` tag is declared ``CDATA`` which means that entities |
|
will not be parsed. Everything until ``</script>`` is handled as script. |
|
This also means that there must never be any ``</`` between the script |
|
tags. ``|tojson`` is kind enough to do the right thing here and |
|
escape slashes for you (``{{ "</script>"|tojson|safe }}`` is rendered as |
|
``"<\/script>"``). |
|
|
|
In Flask 0.10 it goes a step further and escapes all HTML tags with |
|
unicode escapes. This makes it possible for Flask to automatically |
|
mark the result as HTML safe. |
|
|
|
|
|
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 |
|
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 type=text/javascript> |
|
$(function() { |
|
$('a#calculate').bind('click', function() { |
|
$.getJSON($SCRIPT_ROOT + '/_add_numbers', { |
|
a: $('input[name="a"]').val(), |
|
b: $('input[name="b"]').val() |
|
}, function(data) { |
|
$("#result").text(data.result); |
|
}); |
|
return false; |
|
}); |
|
}); |
|
</script> |
|
<h1>jQuery Example</h1> |
|
<p><input type=text size=5 name=a> + |
|
<input type=text size=5 name=b> = |
|
<span id=result>?</span> |
|
<p><a href=# id=calculate>calculate server side</a> |
|
|
|
I won't go into detail here about how jQuery works, just a very quick |
|
explanation of the little bit of code above: |
|
|
|
1. ``$(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. |
|
|
|
If you don't get the whole picture, download the :gh:`sourcecode |
|
for this example <examples/jqueryexample>`.
|
|
|