@narando/negotiate-accepted-language

A custom Accept-Language parser. You can use this package to localize your clients based on the http headers.

Getting Started

You need to have nodejs and npm installed.

$ npm install @narando/negotiate-accepted-language

Usage

Based on the priority the best matching language will be returned.

import negotiateAcceptedLanguage from "@narando/negotiate-accepted-language";

const supportedLanguages = ["de-DE", "en-US"];
const acceptedLanguages = "de-DE,de;q=0.9,en;q=0.8,en-US;q=0.7";

negotiateAcceptedLanguage(supportedLanguages, acceptedLanguages);
// returns "de-DE"

In case no one of the accepted languages will match the supported languages exactly. The function tries to find the closest match. To find the closest match the country tag will be ignored.

import negotiateAcceptedLanguage from "@narando/negotiate-accepted-language";

const supportedLanguages = ["de-AT", "en-US"];
const acceptedLanguages = "de-DE,en-CA;q=0.9";

negotiateAcceptedLanguage (supportedLanguages, acceptedLanguages);
// returns "de-AT"

Usage as express middleware

Implement this function as an express middleware.

import negotiateAcceptedLanguage from "@narando/negotiate-accepted-language";

function getLanguageMiddleware(req, res, next) {
  const supportedLanguages = ["de-DE", "en-US"];
  const acceptedLanguages = req.get("accept-language");

  const language = negotiateAcceptedLanguage(
    supportedLanguages,
    acceptedLanguages
  );

  // Use language with the i18n module of your choice:
  req.i18n.setLanguage(language);
  // Or just save the value to use it later:
  req.language = language;

  next();
}

// Mount as middleware
app.use(getLanguageMiddleware);

Error handling

The function wil return null if the languagesToParse are not supported.

import negotiateAcceptedLanguage from "@narando/negotiate-accepted-language";

const supportedLanguages = ["de-DE", "en-US"];
const acceptedLanguages = "af,ch-ZH;q=0.8";

const matchingLanguage = negotiateAcceptedLanguage(
  supportedLanguages,
  acceptedLanguages
);
// matchingLanguage is null