atril

let.*

Defines a new property in the current scope, assigning the given value.

The reason you need this is because unlike typical expression parsers in frameworks like Angular or Polymer, expressions in atril don't silently swallow references to missing properties. If you try to reference a property that doesn't exist on the viewmodel, it throws an error.

let lets you explicitly define a new property from your view.

Example:

class VM {
  constructor() {
    console.log("I don't know what eidolon means");
  }
}

<div let.eidolon="''">
  <input on.input="eidolon = this.value">
  <p>{{eidolon}}</p>
</div>

Without let or an explicit property definition in the class, this would throw a missing reference error.

let is implemented as a mold, so you can use it on a template tag (only the contents are included into the DOM).

<template let.eidolon="''">
  <input on.input="eidolon = this.value">
  <p>{{eidolon}}</p>
</template>