Using Twig’s default() filter to avoid “Variable some_var does not exist”

References to undefined variables are a common cause of web pages not displaying when using Twig. A simple mention of an undefined variable can cause 500 errors:

{{ some_var }}

Variable some_var does not exist in..

Whilst turning strict_variables off in the twig config will obviously hide the error and is best for production, during development hiding errors can ultimately making spotting bugs harder. A better solution is using Twig’s default() filter like so:

{{ some_var|default("") }}

This will print the variable if it exists or nothing if it is not defined.
For if statements and loops, there are 3 choices:

  1. The default() filter:
  2. {% if some_var|default(false) %}some text{% endif %}
  3. The fine grain but hideously verbose control of defined:
  4. {% if some_var is defined and some_var %}some text{% endif %}
  5. The empty filter:
  6. {% if some_var is not empty %}some text{% endif %}

There are also lots of other useful tests, filters and functions that Twig provides out of the box, check out their documentation pages for more info. Hope this helps. Please like and share if it does 🙂

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