tslint-immutable

tslint-immutable

This repo contains a TSLint version of the eslint-plugin-immutable .

This goal of these TSLint rules are to disable all mutation in TypeScript. Please see the eslint-plugin-immutable version for the rationale beind this.

Installing

npm install tslint-immutable --save-dev

TSLint Rules

There are three rules in the plugin:

no-let

See eslint version for documentation.

no-this

See eslint version for documentation.

no-mutation

See eslint version for documentation.

no-expression-statement

When you call a function and don’t use it’s return value, chances are high that it is being called for its side effect. e.g.

array.push(1)
alert('Hello world!')

This rule checks that the value of an expression is assigned to a variable. However it will still be possible to perform mutations, eg. this rule will not catch these expressions:

const namesWithBar = names.concat([' bar ']) // ok, bound to another variable
return namesWithBar // ok, returned
const newSize = names.push('baz') // maybe `no-unused-vars` can catch this
const newObject = Object.assign(oldObject, { foo: 'bar' }) // tough luck

Supplementary TSLint Rules to Enable

The rules in this package alone can not eliminate mutation in your TypeScript programs. To go the distance I suggest you also enable the following built-in TSLint rules:

• no-var-keyword (self-explanatory)

Sample Configuration File

Here's a sample TSLint configuration file (tslint.json) that activates all the recommended rules:

{
  "rulesDirectory": "path/to/tslint-immutable/rules",
  "rules": {
    "no-let": true,
    "no-this": true,
    "no-mutation": true,
    "no-expression-statement": true,
    "no-var-keyword": true
  }
}