eww/docs/content/main/expression_language.md

+++ title = "Eww expressions" slug = "Embedded eww expression language" weight = 5 +++

The embedded Eww expression-language

Within variable references, you can make use of a small, built-in expression language. This can be used whereever you can use variable-references ({{varname}}).

Example

<button
    class="{{if button_active then 'active' else 'inactive'}}"
    onclick="toggle_thing">
    {{if button_active then 'disable' else 'enable'}}
</button>

Some math: {{12 + 2 * 10}}

Syntax

The expression language supports:

• simple mathematical operations (+, -, *, /, %)
• comparisons (==, !=, >, <)
• boolean operations (||, &&, !)
• elvis operator (?:)
  • if the left side is "", then returns the right side, otherwise evaluates to the left side.
• conditionals (if condition then 'value' else 'other value')
• numbers, strings, booleans and variable references (12, 'hi', true, some_variable)
  • strings can contain other expressions again: 'foo {{some_variable}} bar'
• json access (object.field, array[12], object["field"])
  • for this, the object/array value needs to refer to a variable that contains a valid json string.