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Avoid Duplicated String Literals

Medium
refactoringMaintainability

What is it?​

This practice is triggered by duplicated string literals, which can make the refactoring process error-prone and difficult to maintain. Repeating the same literal string value in multiple places increases the risk of inconsistency if changes are later needed.

Why apply it?​

Duplicated string literals lead to technical debt because any necessary changes must be replicated in every occurrence. Refactoring by replacing these literals with a constant helps centralize updates, reducing the chance of errors and simplifying maintenance.

How to Fix it?​

Replace duplicated string literals with a single constant reference. This practice makes your code cleaner, improves readability, and ensures that any future change to the literal value needs to be made only once.

Exceptions​

To prevent generating some false-positives, literals having less than 10 characters are excluded as well as literals matching /^\w*$/. String literals inside import/export statements and JSX attributes are also ignored. The same goes for statement-like string literals, e.g. 'use strict';.

Examples​

Example 1:​

Negative​

Incorrect implementation that violates the practice.

function prepare(action: string): void {
  console.log("Preparing: " + action);
}

function execute(action: string): void {
  console.log("Executing: " + action);
}

function release(action: string): void {
  console.log("Releasing: " + action);
}

function run(): void {
  prepare("action_to_launch");  // Noncompliant - literal duplicated
  execute("action_to_launch");
  release("action_to_launch");
}

Example 2:​

Positive​

Correct implementation following the practice.

const UNEXPECTED_FAILURE_MSG = "Unexpected failure occurred";

class Logger {
  log(message: string): void {
    console.log("ERROR: " + message);
  }
}

function simulateError(): void {
  new Logger().log(UNEXPECTED_FAILURE_MSG);
  new Logger().log(UNEXPECTED_FAILURE_MSG);
  new Logger().log(UNEXPECTED_FAILURE_MSG);
}

Negative​

Incorrect implementation that violates the practice.

class Logger {
  log(message: string): void {
    console.log("ERROR: " + message);
  }
}

function simulateError(): void {
  new Logger().log("Unexpected failure occurred");  // Noncompliant - literal duplicated
  new Logger().log("Unexpected failure occurred");
  new Logger().log("Unexpected failure occurred");
}

Example 3:​

Positive​

Correct implementation following the practice.

const ACTION_TO_LAUNCH = "action_to_launch";

function prepare(action: string): void {
  console.log("Preparing: " + action);
}

function execute(action: string): void {
  console.log("Executing: " + action);
}

function release(action: string): void {
  console.log("Releasing: " + action);
}

function run(): void {
  prepare(ACTION_TO_LAUNCH); // Compliant
  execute(ACTION_TO_LAUNCH);
  release(ACTION_TO_LAUNCH);
}