| 1 | # Decorators
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| 2 |
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| 3 | Both [event handlers](EventHandlers.md)
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| 4 | and [command handlers](CommandHandlers.md) work
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| 5 | with [TypeScript decorators][decorators]. These identify values that
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| 6 | will be injected into a fresh instance each time the handler runs. If
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| 7 | you're familiar with Spring, this will be particularly intuitive.
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| 8 |
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| 9 | [decorators]: https://www.typescriptlang.org/docs/handbook/decorators.html (TypeScript Decorators)
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| 10 |
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| 11 | Consider the following code within a command handler:
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| 12 |
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| 13 | ```typescript
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| 14 | @Parameter({
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| 15 | displayName: "Desired Spring Boot version",
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| 16 | description: "The desired Spring Boot version across these repos",
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| 17 | pattern: /^.+$/,
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| 18 | validInput: "Semantic version",
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| 19 | required: false,
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| 20 | })
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| 21 | public desiredBootVersion: string = "1.5.6.RELEASE";
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| 22 | ```
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| 23 |
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| 24 | The value of the `desiredBootVersion` parameter (if provided) will be
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| 25 | injected into an instance before the `handle` function is called.
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| 26 |
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| 27 | The decorated variable names the parameter. If you assign a value to
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| 28 | the variable, as in the example, it becomes the parameter’s default
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| 29 | value.
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