Brexpressions

Grammar and parser for Breezy's expressions in brackets.

Expressions

Breezy uses expressions as placeholders that will be substituted with the value when rendered. Expression are very similar to JavaScript property lookups and function calls with the tenary operator. A full expression looks like:

path[.to.method] [args... ] [? truthy] [: falsy]

path is either a direct or dot-separated nested property lookup. args can be any number of (whitespace separated) parameters if the result of the path lookup is a function. Each parameter can either be another path or a sinlge- or doublequoted string. The optional truthy and falsy block can be used to change the return value to another value or string.

Examples:

• Look up the name property:
  • name
• Look up site and get the title:
  • site.title
• Get name and call the toUpperCase string method:
  • name.toUpperCase
• Call the helpers.equal method to check the name against a string:
  • helpers.equal name 'David'
• Call helpers.equal method and return Yes if it matches (null otherwise):
  • helpers.equal name 'David' ? 'Yes'
• Call helpers.equal method and return No if it does not match (null otherwise):
  • helpers.equal name 'David' : 'No'
• Call helpers.equal method and return Yes if and No if it does not match:
  • helpers.equal name 'David' ? 'Yes' : 'No'

helpers.equal simply looks like:

{
  helpers: {
    equal: function(first, second) {
      return first === second;
    }
  }
}

Expressions can be used in Attributes or any other text when wrapped with double curly braces {{}}:

<div show-if="helpers.equal name 'David'">Hi {{name.toUpperCase}} how are you?</div>
<img src="person.png" alt="This person is: {{helpers.equal name 'David' ? 'Dave' : 'I don\'t know'}}">

Note: Dynamically adding attributes like <img {{helpers.equal name 'David' ? 'alt="This is David"'}}> is currently not supported. This can almost always be done in a more HTML-y way, anyway, for example using a custom attribute.