i18n.getMessage()

messageName

string. The name of the message, as specified in the messages.json file. If the message can't be found in messages.json:

• Firefox returns "" and logs an error.
• Chrome returns "" and does not log an error.

substitutions Optional

string or array of string. A single substitution string, or an array of substitution strings.

In Chrome, if you supply more than 9 substitution strings, getMessage() will return undefined.

string. Message localized for current locale.

Get the localized string for "messageContent", with target.url substituted:

let message = browser.i18n.getMessage("messageContent", target.url);
console.log(message);

This would work with a _locales/en/messages.json file containing:

{
  "messageContent": {
    "message": "You clicked $URL$.",
    "description": "Tells the user which link they clicked.",
    "placeholders": {
      "url": {
        "content": "$1",
        "example": "https://developer.mozilla.org"
      }
    }
  }
}

If target.url is "https://developer.mozilla.org", then the value of message, in the "en" locale, would be:

"You clicked https://developer.mozilla.org."

• menu-accesskey-visible
• menu-demo
• notify-link-clicks-i18n