The Ghost folks have a great implementation:

/**

• Defines a property similarly to Ember.computed.oneway,
• save that while a oneway loses its binding upon being set,
• the BoundOneWay will continue to listen for upstream changes.
• This is an ideal tool for working with values inside of {{input}}
• elements.
• @param transform: a function to transform the upstream value. */ var BoundOneWay = function (upstream, transform) { if (typeof transform !== 'function') { //default to the identity function transform = function (value) { return value; }; } return Ember.computed(upstream, function (key, value) { return arguments.length > 1 ? value : transform(this.get(upstream)); }); };

export default BoundOneWay;