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Having a bidirectional computed property on an EmberJS text field


We had an issue where we had an EmberJS model with an attribute time, but we wanted to display this as a human-readable time that was also user-editable.

We couldn't just add a computed property and use an {{input valueBinding="..."}}, because valueBinding is one directional only (if we change the TextField, it may change the computed property but this computed property will not change the original property). It seemed too messy to create a new model property timeHumanReadable that would then be updated accordingly - we only want to store the original time for API purposes.

The solution was to first create a computed property timeHumanReadable on the original Ember model:

App.MyModel = DS.Model.extend
  # this HAS to be format '11:00'
  time: DS.attr('string', {
    defaultValue: moment(new Date()).format("HH:mm")

  timeHumanReadable: ( ->
    moment(@get("time"), "HH:mm").format("h:mma")

And then create a new View called TextFieldTime, which would get a reference to the original model object and update times accordingly:

App.TextFieldTime = Ember.TextField.extend
  init: ->
    @model = @get("parentView").get("context").get("content")

  focusOut: ->
    # we first convert the human time into HH:mm, and then display the reformatted human time
    converted = App.TimeHelper.convert(@value, moment().format("HH:mm"))
    @model.set('time', converted)
    # setting 'time' in focusOut doesn't seem to update listening properties, and setting it through @$().val
    # will not persist across page transitions, so we just update the computed property directly - seems to work
    @model.set('timeHumanReadable', moment(converted, 'HH:mm').format('h:mma'))

Finally, using this in a Handlebars template:

{{view App.TextFieldTime valueBinding="timeHumanReadable" isVisibleBinding="isNormalTime" class="my-time-input-class"}}

Categories: Javascript
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Last edited by jevon jevon 37 months ago