loop-protect

JS Bin's loop protection implementation as a reusable library.

This code protects use cases where user code includes an infinite loop using a while, for or do loop. It also prevents infinite loops from being created when a React component references itself.

Note that this does not solve the halting problem but simply rewrites JavaScript (using Babel's AST) wrapping loops with a conditional break. This also does not protect against recursive loops in general, just React components.

Example

With loop protection in place, it means that a user can enter the code as follows on JS Bin, and the final console.log will still work.

The code is transformed from this:

``js
while (true) {
doSomething();
}

console.log('All finished');
`

…to this:

`js
var _LP = Date.now();
while (true) {
if (Date.now() - _LP > 100)
break;

doSomething();
}

console.log('All finished');
`

Usage

The loop protection is a babel transform, so can be used on the server or in the client.

The previous implementation used an injected library to handle tracking loops - this version does not.

$3

`js
import Babel from 'babel-standalone';
import protect from 'loop-protect';

const timeout = 100; // defaults to 100ms
Babel.registerPlugin('loopProtection', protect(timeout));

const transform = source => Babel.transform(source, {
plugins: ['loopProtection'],
}).code;

// rewrite the user's JavaScript to protect loops
var processed = transform(getUserCode());

// run in an iframe, and expose the loopProtect variable under a new name
var iframe = getNewFrame();

// append the iframe to allow our code to run as soon as .close is called
document.body.appendChild(iframe);

// open the iframe and write the code to it
var win = iframe.contentWindow;
var doc = win.document;
doc.open();

doc.write('