optional() function

@microsoft/fast-element/di.js > optional

optional() function

A decorator that allows you to optionally inject a dependency depending on whether the [[Key]] is present, for example:

Signature:

optional: (key: any) => any

Parameters

Parameter	Type	Description
key	any	The key to optionally resolve. see on interactions with interfaces

Returns:

any

Example 1

class Foo {
  constructor( @inject('mystring') public str: string = 'somestring' )
}
container.get(Foo); // throws

would fail

Example 2

class Foo {
  constructor( @optional('mystring') public str: string = 'somestring' )
}
container.get(Foo).str // somestring

if you use it without a default it will inject undefined, so remember to mark your input type as possibly undefined!