Formatting of dates and times in Flask templates using moment.js.

Last update: Nov 28, 2022

Overview

Flask-Moment

This extension enhances Jinja2 templates with formatting of dates and times using moment.js.

Quick Start

Step 1: Initialize the extension:

from flask_moment import Moment
moment = Moment(app)

Step 2: In your <head> section of your base template add the following code:

<head>
    {{ moment.include_jquery() }}
    {{ moment.include_moment() }}
</head>

This extension also supports the Flask application factory pattern by allowing you to create a Moment object and then separately initialize it for an app:

    moment = Moment()

    def create_app(config):
        app = Flask(__name__)
        app.config.from_object(config)
        # initialize moment on the app within create_app()
        moment.init_app(app)

    app = create_app(prod_config)

Note that jQuery is required. If you are already including it on your own then you can remove the include_jquery() line. Secure HTTP is always used to request the external js files..

The include_jquery() and include_moment() methods take some optional arguments. If you pass a version argument to any of these two calls, then the requested version will be loaded from the default CDN. If you pass local_js, then the given local path will be used to load the library. The include_moment() argument takes a third argument no_js that when set to True will assume that the Moment JavaScript library is already loaded and will only add the JavaScript code that supports this extension.

Step 3: Render timestamps in your template. For example:

<p>The current date and time is: {{ moment().format('MMMM Do YYYY, h:mm:ss a') }}.</p>
<p>Something happened {{ moment(then).fromTime(now) }}.</p>
<p>{{ moment(then).calendar() }}.</p>

In the second and third examples template variables then and now are used. These must be instances of Python's datetime class, and must be "naive" objects. See the documentation for a discussion of naive date and time objects. As an example, now can be set as follows:

now = datetime.utcnow()

By default the timestamps will be converted from UTC to the local time in each client's machine before rendering. To disable the conversion to local time pass local=True.

Note that even though the timestamps are provided in UTC the rendered dates and times will be in the local time of the client computer, so each users will always see their local time regardless of where they are located.

Function Reference

The supported list of display functions is shown below:

moment(timestamp=None, local=False).format(format_string=None)
moment(timestamp=None, local=False).fromNow(no_suffix=False)
moment(timestamp=None, local=False).fromTime(another_timesatmp, no_suffix=False)
moment(timestamp=None, local=False).toNow(no_suffix=False)
moment(timestamp=None, local=False).toTime(another_timesatmp, no_suffix=False)
moment(timestamp=None, local=False).calendar()
moment(timestamp=None, local=False).valueOf()
moment(timestamp=None, local=False).unix()

Consult the moment.js documentation for details on these functions.

Auto-Refresh

All the display functions take an optional refresh argument that when set to True will re-render timestamps every minute. This can be useful for relative time formats such as the one returned by the fromNow() or fromTime() functions. By default refreshing is disabled.

Default Format

The format() function can be invoked without arguments, in which case a default format of ISO8601 defined by the moment.js library is used. If you want to set a different default, you can set the MOMENT_DEFAULT_FORMAT variable in the Flask configuration. Consult the moment.js format documentation for a list of accepted tokens.

Internationalization

By default dates and times are rendered in English. To change to a different language add the following line in the <head> section after the include_moment() line:

{{ moment.locale("es") }}

The above example sets the language to Spanish. Moment.js supports a large number of languages, consult the documentation for the list of languages and their two letter codes.

The extension also supports auto-detection of the client's browser language:

{{ moment.locale(auto_detect=True) }}

Custom locales can also be included as a dictionary:

{{ moment.locale(customizations={ ... }) }}

See the Moment.js locale customizations documentation for details on how to define a custom locale.

Ajax Support

It is also possible to create Flask-Moment timestamps in Python code, for cases where a template is not used. This is the syntax:

timestamp = moment.create(datetime.utcnow()).calendar()

The moment variable is the Moment instance that was created at initialization time.

A timestamp created in this way is an HTML string that can be returned as part of a response. For example, here is how a timestamp can be returned in a JSON object:

return jsonify({ 'timestamp': moment.create(datetime.utcnow()).format('L') })

The Ajax callback in the browser needs to call flask_moment_render_all() each time an element containing a timestamp is added to the DOM. The included application demonstrates how this is done.

Subresource Integrity(SRI)

SRI is a security feature that enables browsers to verify that resources they fetch are not maliciously manipulated. To do so a cryptographic hash is provided that proves integrity.

SRI is enabled by default. If you wish to use another version or want to host your own javascript, a separate hash can be provided. Just add sri=<YOUR-HASH> when calling either moment.include_moment() or moment.include_jquery(). If no sri hash is provided and you choose to use a non default version of javascript, no sri hash will be added.

You can always choose to disable sri. To do so just set sri=False.

Development

Currently the tests are written using pytest.

pip install pytest

To run the tests from the root directory use: py.test.

Reports on coverage with missing line numbers can be generated using pytest-cov:

pip install pytest-cov

And then running: py-test --cov-report term-missing --cov=flask_moment

Formatting of dates and times in Flask templates using moment.js.

Related tags

Overview

Flask-Moment

Quick Start

Function Reference

Auto-Refresh

Default Format

Internationalization

Ajax Support

Subresource Integrity(SRI)

Development

Owner

Miguel Grinberg

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