src/lib/Messages.js


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"use strict";
{
  let handlers = new Set();

  let dispatch = async (msg, sender) => {
    let {_messageName} = msg;
    let answers = [];
    for (let h of handlers) {
      let f = h[_messageName];
      if (typeof f === "function") {
        answers.push(f(msg, sender));
      }
    }
    if (answers.length) {
      return await (
        answers.length === 1 ? answers.pop(): Promise.all(answers)  
      );
    }
    console.log("Answering %s", _messageName);
    return undefined;
  };
  
  var Messages = {
    addHandler(handler) {
      let originalSize = handlers.size;
      handlers.add(handler);
      if (originalSize === 0 && handlers.size === 1) {
        browser.runtime.onMessage.addListener(dispatch);
      }
    },
    removeHandler(handler) {
      let originalSize = handlers.size;
      handlers.delete(handler);
      if (originalSize === 1 && handlers.size === 0) {
        browser.runtime.onMessage.removeListener(dispatch);
      }
    },
    async send(name, args = {}, toContent = null) {
      args._messageName = name;
      if (toContent && "tabId" in toContent) {
        let opts;
        if ("frameId" in toContent) opts = {frameId: toContent.frameId};
        return await browser.tabs.sendMessage(toContent.tabId, args, opts);
      }
      return await browser.runtime.sendMessage(args);
    }
  }
}