(function(root, mod) {
  if (typeof exports == "object" && typeof module == "object") // CommonJS
    return mod(exports);
  if (typeof define == "function" && define.amd) // AMD
    return define(["exports"], mod);
  mod((root.tern || (root.tern = {})).signal = {}); // Plain browser env
})(this, function(exports) {

  function on(type, f) {
    var handlers = this._handlers || (this._handlers = Object.create(null));
    (handlers[type] || (handlers[type] = [])).push(f);
  }

  function off(type, f) {
    var arr = this._handlers && this._handlers[type];
    if (arr) for (var i = 0; i < arr.length; ++i)
      if (arr[i] == f) { arr.splice(i, 1); break; }
  }

  var noHandlers = []
  function getHandlers(emitter, type) {
    var arr = emitter._handlers && emitter._handlers[type];
    return arr && arr.length ? arr.slice() : noHandlers
  }

  function signal(type, a1, a2, a3, a4) {
    var arr = getHandlers(this, type)
    for (var i = 0; i < arr.length; ++i) arr[i].call(this, a1, a2, a3, a4)
  }

  function signalReturnFirst(type, a1, a2, a3, a4) {
    var arr = getHandlers(this, type)
    for (var i = 0; i < arr.length; ++i) {
      var result = arr[i].call(this, a1, a2, a3, a4)
      if (result) return result
    }
  }

  function hasHandler(type) {
    var arr = this._handlers && this._handlers[type]
    return arr && arr.length > 0 && arr
  }

  exports.mixin = function(obj) {
    obj.on = on; obj.off = off;
    obj.signal = signal;
    obj.signalReturnFirst = signalReturnFirst;
    obj.hasHandler = hasHandler;
    return obj;
  };
});