ESLint rules for identifying duplicate string literals.

Typical JS minifiers, such as UglifyJS, don't touch string literals. For instance, running the following code through Uglify:

function maybeLog(something) {
  if (something === 'a string literal') {
    console.log('a string literal');
  }

  return something || 'a string literal';
}

Will yield:

function maybeLog(o){return"a string literal"===o&&console.log("a string literal"),o||"a string literal"}

If you're trying to squeeze everything you can out of your minifcation process and slim down your bundles, you can simply pull those literals into a single variable definition so Uglify can handle it appropriately:

function maybeLog(something) {
  const foo = 'a string literal';

  if (something === foo) {
    console.log(foo);
  }

  return something || foo;
}

Will now yield:

function maybeLog(o){const n="a string literal"
return o===n&&console.log(n),o||n}

In this simple example we saved 12 bytes. That may not seem like much, but in a large project the savings will be much greater. That's where this plugin can be useful.

First, install ESLint:

$ npm install eslint --save-dev

Next, install eslint-plugin-no-dupe-literals:

$ npm install eslint-plugin-no-dupe-literals --save-dev

Add no-dupe-literals to the plugins section of your .eslintrc:

{
  "plugins": [
    "no-dupe-literals"
  ]
}

Then configure the rules:

{
  "rules": {
    "no-dupe-literals/in-scope": "warn"
  }
}

This plugin currently only supports one rule, in-scope, which allows you to check for duplicate string literals at the scope level.