Expressions

Expressions in altr are a combination of [values lookups], [operations], and [filters] which watch for changes and report any changes to their resulting value. Expressions can be used in several places, in any textContent in your template, in attributes, and as arguments to most tags.

To use an expression in textContent, simple place the expression between double currly braces (eg. {{ my_value }}).

  • {% tab %}

altr(document.body, {my_value: “hello, World!”})

{{ my_value }}

altr will do a lookup of a variable name my_value in when either of the following are true: - {{ my_value }} appears in any DOM node’s textContent or in any DOM node attribute that is not prefixed by altr. - DOM attribute matches altr-attr-*="my_value".

The altr-attr-my-attribute="my_value" syntax will set the my-attribute attribute on the DOM node to whatever my_value evaluates to in the current template context. When the template context is updated, this will update as well. If my_value evaluates to null, undefined or false, then my-attribute will simply be excluded, which is useful for boolean attributes such as checked (which can also have a value), or for SVG elements which will throw errors for illegal values.

Template variable lookups are backed by [dirtybit][dirtybit]. dirtybit supports dot-path lookups, literals, a wide range of operators, as well as filters. See the documentation for more details.

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