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rxjs-tslint-rules

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Readme

rxjs-tslint-rules

What is it?

rxjs-tslint-rules is small set of TSLint rules to help manage projects that use rxjs/add/... imports and to highlight other potential problems.

Why might I need it?

When using imports that patch Observable:

import { Observable } from "rxjs/Observable";
import from "rxjs/add/observable/of";
import from "rxjs/add/operator/map";

TypeScript will see the merged declarations in all modules, making it difficult to find rxjs/add/... imports that are missing from modules in which patched observables and operators are used.

This can cause problems, as whether or not Observable is patched then depends upon the order in which the modules are executed.

The rules in this package can be used to highlight missing - or unused - imports and other potential problems with RxJS.

Install

Install the package using NPM:

npm install rxjs-tslint-rules --save-dev

Update your tslint.json file to extend this package:

{
  "extends": [
    "rxjs-tslint-rules"
  ],
  "rules": {
    "rxjs-add": { "severity": "error" },
    "rxjs-no-unused-add": { "severity": "error" }
  }
}

Rules

The package includes the following rules:

Rule	Description	Options
`rxjs-add`	Enforces the importation of patched observables and operators used in the module.	See below
`rxjs-no-add`	Disallows the importation of patched observables and operators.	None
`rxjs-no-do`	I do without `do` operators. Do you not?	None
`rxjs-no-patched`	Disallows the calling of patched methods. Operators must be imported and called explicitly - not via the `Observable` prototype.	None
`rxjs-no-subject-unsubscribe`	Disallows the calling of `unsubscribe` directly upon `Subject` instances. For an explanation of why this can be a problem, see this Stack Overflow answer.	None
`rxjs-no-unused-add`	Disallows the importation of patched observables or operators that are not used in the module.	None
`rxjs-no-wholesale`	Disallows the wholesale importation of `rxjs` or `rxjs/Rx`.	None

Options

The rxjs-add rule takes an optional object with the property file. This is the path of the module - relative to the tsconfig.json - that imports the patched observables and operators.

For example:

"rules": {
  "rxjs-add": {
    "options": [{
      "allowElsewhere": false,
      "allowUnused": false,
      "file": "./source/rxjs-imports.ts"
    }],
    "severity": "error"
}

Specifying the file option allows all of the patched observables and operators to be kept in a central location. Said module should be imported before other modules that use patched observables and operators. The importation of said module is not enforced; the rule only ensures that it imports observables and operators that are used in other modules.

If file is specified, the allowElsewhere and allowUnused options can be used to configure whether or not patched imports are allowed in other files and whether or not unused patched imports are allowed. Both allowElsewhere and allowUnused default to false.

Note that there is no file option for the rxjs-no-unused-add rule, so that rule should not be used in conjunction with the rxjs-add rule - if the file option is specified for the latter. Use the rxjs-add rule's allowUnused option instead.

If the file option is not specified, patched observables and operators must be imported in the modules in which they are used.

Gotchas

`Observable.create`

Observable.create is declared as a Function, which means that its return type is any. This results in an observable that's not seen by the rules, as they use TypeScript's TypeChecker to determine whether or not a call involves an observable.

The rule implementations include no special handling for this case, so if spurious errors are effected due to Observable.create, explicit typing can resolve them. For example:

const ob: Observable<number> = Observable.create((observer: Observer<number>) => { ...