There are some things you don't want to forget when working with Nest dependency injection.
The Nest DI is declarative and if you forget to provide an injectable you wont see an error until run time. Nest is good at telling you where these are but sometimes it's not.
In particular if you're using custom providers the errors can be really tricky to figure out because they won't explicitly error about mismatched injected items, you will just get unexpected operation.
These are described in the "Common Errors" section of the nest js docs.
When working with NestJS I generate my front end client and models using the swagger generated from the nest controllers and models.
I have a bunch of rules here that are mostly for strict typing with decorators for those controllers and models.
These rules are somewhat opinionated, but necessary for clean model generation if using an Open Api model generator.
Nest Modules
- provided-injected-should-match-factory-parameters
- injectable-should-be-provided
Nest Swagger
- api-property-matches-property-optionality
- controllers-should-supply-api-tags
- api-method-should-specify-api-response
- api-enum-property-best-practices
- api-property-returning-array-should-set-array
npm install --save-dev @darraghor/eslint-plugin-nestjs-typed
Then update your eslint with the plugin import and add the recommended rule set
module.exports = {
env: {
es6: true,
},
extends: ["plugin:@darraghor/nestjs-typed/recommended"],
parser: "@typescript-eslint/parser",
parserOptions: {
project: ["./tsconfig.json"],
sourceType: "module",
ecmaVersion: "es2019",
},
plugins: ["@darraghor/nestjs-typed"],
};Note: the injectables test scans your whole project. It's best to filter out ts things that don't matter - use filterFromPaths configuration setting for this. There are some defaults already applied. See details below.
Note: You can easily turn off all the swagger rules if you don't use swagger by adding the no-swagger rule set AFTER the recommended rule set.
// all the other config
extends: ["plugin:@darraghor/nestjs-typed/recommended",
"plugin:@darraghor/nestjs-typed/no-swagger"
],
// more configChecks that there are the same number of injected items in a Provider that are passed to the factory method
Passes (Myservide injected and myservice used in factory params)
export const MyOtherInjectableProvider: NotAProvider = {
provide: MyOtherInjectable,
useFactory: async (config: MyService): Promise<MyOtherInjectable> => {
return new MyOtherInjectable();
},
inject: [MyService],
};Fails (SecondService is not used in the factory)
export const MyOtherInjectableProvider: Provider = {
provide: MyOtherInjectable,
useFactory: async (config: MyService): Promise<MyOtherInjectable> => {
return new MyOtherInjectable();
},
inject: [MyService, SecondService],
};Checks that a class marked with @Injectable is injected somewhere or used in a provider.
Fails if a thing marked as @Injectable is not in the providers of a module or provides in a provider.
There is some additional configuration you can provide for this rule. This is the default setting. You should overrride this with your src directory and any strings to filter out from paths (note that the filterFromPaths are NOT globs - just matched strings).
"@darraghor/nestjs-typed/injectable-should-be-provided": [
"error",
{
src: ["src/**/*.ts"],
filterFromPaths: ["node_modules", ".test.", ".spec."],
},
],This checks that you have added the correct api property decorator for your swagger documents.
There are specific decorators for optional properties and using the correct one affects Open Api generation.
The following FAILS because this is an optional property and should have @ApiPropertyOptional
class TestClass {
@Expose()
@ApiProperty()
thisIsAStringProp?: string;
}The following FAILS because this is a required property and should have @ApiProperty
class TestClass {
@Expose()
@ApiPropertyOptional()
thisIsAStringProp!: string;
}If you have more than a handful of api methods the swagger UI is difficult to navigate. It's easier to group api methods by using tags.
This PASSES because it has api tags
@ApiTags("my-group-of-methods")
@Controller("my-controller")
class TestClass {}The following FAILS because it's missing api tags
@Controller("my-controller")
class TestClass {}If you have an api method like @Get() you should specify the return status code (and type!) by using @ApiResponse and the other expected responses. I often leave out 400s and 500s because it's kind of assumed but they should be used if the return type changes!
This PASSES
class TestClass {
@Get()
@ApiResponse({status: 200, type: String})
@ApiBadRequestResponse({description: "Bad Request"})
public getAll(): Promise<string[]> {
return [];
}
}The following FAILS because it's missing api response decorators
class TestClass {
@Get()
public getAll(): Promise<string[]> {
return [];
}
}If you use enums on properties you should set the correct open api properties in the ApiProperty decorator.
If you don't use enum open api won't use the enum correctly.
If you don't use enumName then Open api will create a new enum for each api method. This is awful to use in a generated client.
You don't need to use type: any more. This used to be necessary in old versions to get enum strings correctly output.
The enumName should match the enum type you specify. It's easier to match them up when working on BE and FE. And it reduces chance for typos resulting in duplicate enums.
This is a perfect enum description
class TestClass {
@ApiPropertyOptional({enum: MyEnum, enumName: "MyEnum"})
thisIsAnEnumProp?: MyEnum;
}Fails - you don't need type
class TestClass {
@ApiPropertyOptional({type: MyEnum, enum: MyEnum, enumName: "MyEnum"})
thisIsAnEnumProp?: MyEnum;
}Fails - you need to add a name
class TestClass {
@ApiPropertyOptional({enum: MyEnum})
thisIsAnEnumProp?: MyEnum;
}Fails - the enumName doesn't match the enumType
class MyClass {
@ApiProperty({enumName: "MyEnumTYPO", enum: MyEnum})
public myProperty!: MyEnum;
}If you return an array you should indicate this in the api property. There are two ways to do this
ApiProperty({type:[String]}) OR ApiProperty({type:String, isArray:true})
I enforce the second long way! You can turn this off if you prefer the shorthand way but you won't get warned if you missed the array specification.
This passes
class TestClass {
@ApiPropertyOptional({enumName: "MyEnum" isArray:true})
thisIsAProp!: MyEnum[];
}This passes
class TestClass {
@ApiPropertyOptional({type: String, isArray: true})
thisIsAProp!: Array<string>;
}This FAILS - missing isArray
class TestClass {
@ApiPropertyOptional({type: String})
thisIsAProp!: Array<string>;
}This FAILS - doesn't need isArray
class TestClass {
@ApiPropertyOptional({type: String, isArray: true})
thisIsAProp!: string;
}