Function Optional

If the identifier cannot be found, substitute it with null.

The constraints supported are listed in ResolutionConstraintFlag.

Example

This function can be used to construct a bitmask for use in the dependencies array of a service. While this can be used publicly, it is mainly for use within TypeDI; it allows you to configure specific constraints for use when resolving a specific service.

const constraintBitMask = Optional() | Self();

if (constraintBitMask & ResolutionConstraintFlag.Optional) {
  console.log('The dependency is optional.');
}
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Example

Here is an example of this constraint as part of a service declaration:

const NAME = new Token<string>();

@Service([
  [NAME, Optional()]
])
class MyService {
  constructor (private name: string | null) {
    // If "NAME" isn't provided in the container the service is run under,
    // it will be substituted with null.  Note that the container may not
    // be the exact one it was declared under, but a descendent.
  }
}
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See

ResolutionConstraintFlag