Class Helper

public

Ember Helpers are functions that can compute values, and are used in templates. For example, this code calls a helper named format-currency:

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<div>{{format-currency cents currency="$"}}</div>

Additionally a helper can be called as a nested helper (sometimes called a subexpression). In this example, the computed value of a helper is passed to a component named show-money:

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{{show-money amount=(format-currency cents currency="$")}}

Helpers defined using a class must provide a compute function. For example:

currency.js
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import Helper from '@ember/component/helper';

export default Helper.extend({
  compute(params, hash) {
    let cents = params[0];
    let currency = hash.currency;
    return `${currency}${cents * 0.01}`;
  }
});

Each time the input to a helper changes, the compute function will be called again.

As instances, these helpers also have access to the container an will accept injected dependencies.

Additionally, class helpers can call recompute to force a new computation.

Show:

params
Array
The positional arguments to the helper
hash
Object
The named arguments to the helper

Override this function when writing a class-based helper.

On a class-based helper, it may be useful to force a recomputation of that helpers value. This is akin to rerender on a component.

For example, this component will rerender when the currentUser on a session service changes:

email.js
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import Helper from '@ember/component/helper'
import { inject as service } from '@ember/service'
import { observer } from '@ember/object'

export default Helper.extend({
  session: service(),
  onNewUser: observer('session.currentUser', function() {
    this.recompute();
  }),
  compute() {
    return this.get('session.currentUser.email');
  }
});