Scope follows a function. Creating a simple state object.

scopeFollowingAFunction.js

var createIdempotentWorker = function() {
  var isWorking = false;
  
  return {
    doWork: function() {
      if (isWorking) {
        console.log("I'm already working");
        return;
      }
      isWorking = true;
      console.log("Starting work");
    }
  };
};

worker = createIdempotentWorker(); //everytime this function is called, a new local scope is created on line 2

//call #1 - worker.doWork() //output: "Starting work"
//call #2 - worker.doWork() //output: "I'm already working"

callCallback = function (cb) {
  cb();
};

// scope gets carried around with the function
callCallback(worker.doWork); //output: "Starting work"
callCallback(worker.doWork); //output: "I'm already working"