is defined twig template code example

Example 1: twig is set variable

{# defined works with variable names #}
{% if foo is defined %}
    ...
{% endif %}

{# and attributes on variables names #}
{% if foo.bar is defined %}
    ...
{% endif %}

{% if foo['bar'] is defined %}
    ...
{% endif %}

Example 2: twig if

{% if online == false %}
    <p>Our website is in maintenance mode. Please, come back later.</p>
{% endif %}