Ember.Helper Class
Ember Helpers are functions that can compute values, and are used in templates.
For example, this code calls a helper named format-currency
:
<div>{{format-currency cents currency="$"}}</div>
Additionally a helper can be called as a nested helper (sometimes called a
subexpression). In this example, the computed value of a helper is passed
to a component named show-money
:
{{show-money amount=(format-currency cents currency="$")}}
Helpers defined using a class must provide a compute
function. For example:
export default Ember.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.
Methods
compute
-
params
-
hash
Override this function when writing a class-based helper.
Parameters:
-
params
ArrayThe positional arguments to the helper
-
hash
ObjectThe named arguments to the helper
helper
-
helper
In many cases, the ceremony of a full Ember.Helper
class is not required.
The helper
method create pure-function helpers without instances. For
example:
// app/helpers/format-currency.js
export default Ember.Helper.helper(function(params, hash) {
let cents = params[0];
let currency = hash.currency;
return ${currency}${cents * 0.01}
;
});
Parameters:
-
helper
FunctionThe helper function
recompute
()
public
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:
// app/helpers/current-user-email.js
export default Ember.Helper.extend({
session: Ember.inject.service(),
onNewUser: Ember.observer('session.currentUser', function() {
this.recompute();
}),
compute() {
return this.get('session.currentUser.email');
}
});