babel-plugin-transform-prune-unused-imports

babel-plugin-transform-prune-unused-imports

Install

Using npm:

npm install babel-plugin-transform-prune-unused-imports --save-dev

or using yarn:

yarn add babel-plugin-transform-prune-unused-imports --dev

Usage

Options

By default, only true and false identifiers are considered truthy/falsy.

• falsyExpressions : Array<string> - Expressions (in addition to false) to be treated as falsy
• truthyExpressions : Array<string> - Expressions (in addition to true) to be treated as truthy

Examples

{
  "plugins": [
    [
      "transform-prune-unused-imports",
      {
        "falsyExpressions": ["process.env.NODE_ENV !=='production'"]
      }
    ]
  ]
}

{
  "plugins": [
    [
      "transform-prune-unused-imports",
      {
        "falsyExpressions": ["__NODE__"],
        "truthyExpressions": ["__BROWSER__"]
      }
    ]
  ]
}

Features

This plugin is able identify unused imports in the following scenarios:

Unreachable conditionals

import { unreachable, reachable } from "some-pkg";

if (false) {
  unreachable;
}

if (true) {
  reachable;
} else {
  unreachable;
}

true ? reachable : unreachable;

false ? unreachable : reachable;

Unreachable chained logical expressions

import { unreachable } from "some-pkg";

foo && false && bar && unreachable;

Variable shadowing

Variable scope is correctly handled.

// Before
import { unused } from "some-pkg";

function foo(unused) {
  unused;
}

// After
function foo(unused) {
  unused;
}

Caveats

While this plugin works for most use cases, the static analysis is performed by this plugin is ultimately limited and won't work in some scenarios.

Unused assignment expressions

Currently this plugin will not prune unused imports that are assigned to variables, even if those new variables are unused. For example:

import { unreachable } from "some-pkg";

const foo = unreachable;

if (false) {
  foo;
}