emitter.js

'use strict';

var atoa = require('atoa');
var debounce = require('./debounce');

module.exports = function emitter (thing, options) {
  var opts = options || {};
  var evt = {};
  if (thing === undefined) { thing = {}; }
  thing.on = function (type, fn) {
    if (!evt[type]) {
      evt[type] = [fn];
    } else {
      evt[type].push(fn);
    }
    return thing;
  };
  thing.once = function (type, fn) {
    fn._once = true; // thing.off(fn) still works!
    thing.on(type, fn);
    return thing;
  };
  thing.off = function (type, fn) {
    var c = arguments.length;
    if (c === 1) {
      delete evt[type];
    } else if (c === 0) {
      evt = {};
    } else {
      var et = evt[type];
      if (!et) { return thing; }
      et.splice(et.indexOf(fn), 1);
    }
    return thing;
  };
  thing.emit = function () {
    var args = atoa(arguments);
    return thing.emitterSnapshot(args.shift()).apply(this, args);
  };
  thing.emitterSnapshot = function (type) {
    var et = (evt[type] || []).slice(0);
    return function () {
      var args = atoa(arguments);
      var ctx = this || thing;
      if (type === 'error' && opts.throws !== false && !et.length) { throw args.length === 1 ? args[0] : args; }
      et.forEach(function emitter (listen) {
        if (opts.async) { debounce(listen, args, ctx); } else { listen.apply(ctx, args); }
        if (listen._once) { thing.off(type, listen); }
      });
      return thing;
    };
  };
  return thing;
};