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protex is like a mutex but for Promises. That is, an instance executes one promise at a time and remains locked until the Promise is resolved.


var protex = require('protex')();
protex.isLocked(); // => false 
// Submit a promise chain for execution. 
// The protex instance will remain locked until the returned promise is fulfilled. 
var promise = protex.exec(function() {
    return Promise.resolve()
        .then(function() {
            try {
                protex.exec(function() {
                    console.log("i won't run");
            } catch (e) {
                protex.isLocked(); // => true 
promise.then(function() {
    console.log("protex is now unlocked!");



Get it:

npm install protex

Require it:

var protex = require('protex');

UMD etc.

Copy and paste build/protex.js or build/protex.min.js to your project.


var prx = protex()

Create a new protex.


Returns true if currently locked, false otherwise.


Submit thing for execution. Throws an exception if currently locked.

thing can be either a function or a Promise, although functions are preferred - the reason being that Promises begin to execute the moment they are created, i.e. before prx.exec() is called, meaning that it's possible to circumvent the lock. Passing a function will correctly delay the instantation of the Promise until prx.exec() has been called and locking is complete.

If thing is a function and it doesn't return a Promise it is assumed that the function is synchronous and the protex is unlocked immediately after the call returns.

Copyright & License

© 2014 Jason Frame [ @jaz303 / ]

Released under the ISC license.