Code snippet for mutual exclusion lock in javascript.

FastMutex.js

FastMutex.prototype.runInLock = function (callback, opt_context) {
  this._setX()

  if (!this._isLockAvailable()) {
    this._retry(callback, opt_context)
    return
  }

  this._setY()

  if (this._getX() != this._clientId) {
    window.setTimeout(function () {
      if (this.hasLock()) this._execute(callback, opt_context)
      else this._retry(callback, opt_context)
    }.bind(this), Math.round(Math.random() * 100))

  } else {
    this._execute(callback, opt_context)
  }
}

FastMutex.prototype._execute = function (callback, opt_context) {
  var rv
  try {
    rv = callback.call(opt_context)
  } finally {
    if (rv instanceof goog.async.Deferred) {
      rv.addFinally(this._clearLock, this)
    } else {
      this._clearLock()
    }
  }
}