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Built-in Helpers

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In the last section you learned how to write a helper. A helper is usually a simple function that can be used in any template. Ember comes with a few helpers that can make developing your templates a bit easier. These helpers can allow you to be more dynamic in passing data to another helper or component.

Using a helper to get a property dynamically

The {{get}} helper makes it easy to dynamically send the value of a variable to another helper or component. This can be useful if you want to output one of several values based on the result of a computed property.

{{get this.address this.part}}

if the part computed property returns "zip", this will display the result of this.address.zip. If it returns "city", you get this.address.city.

Nesting built-in helpers

In the last section it was discussed that helpers can be nested. This can be combined with these sorts of dynamic helpers. For example, the {{concat}} helper makes it easy to dynamically send a number of parameters to a component or helper as a single parameter in the format of a concatenated string.

{{get "foo" (concat "item" this.index)}}

This will display the result of this.foo.item1 when index is 1, and this.foo.item2 when index is 2, etc.

Built-in block helpers

Now let's say your template is starting to get a bit cluttered and you now want to clean up the logic in your templates. This can be achieved with the let block helper. The {{let}} helper lets you create new bindings in your template.

Say your template now looks like this:

Welcome back {{concat (capitalize this.person.firstName) ' ' (capitalize this.person.lastName)}}

Account Details:
First Name: {{capitalize this.person.firstName}}
Last Name: {{capitalize this.person.lastName}}

As mentioned in the previous section we use the concat helper to render both person.firstName and person.lastName in one go. But we also want to make sure that the names are capitalized. It gets a bit repetitive to keep writing capitalize and honestly, we might just forget it at some point. Thankfully, we can use the {{let}} helper to fix this:

{{#let (capitalize this.person.firstName) (capitalize this.person.lastName)
  as |firstName lastName|
}}
  Welcome back {{concat firstName ' ' lastName}}

  Account Details:
  First Name: {{firstName}}
  Last Name: {{lastName}}
{{/let}}

Now, as long as your template is wrapped in the let helper you can access the capitalized first name and last name as firstName and lastName instead of (capitalize this.person.firstName).

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