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.

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.

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:

while (true) {
  doSomething();
}
 
console.log('All finished');

…to this:

let i = 0;
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.

Example (client) implementation

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('<script>' + processed + '<' + '/script>');
doc.close();
 
// code now runs, and if there's an infinite loop, it's cleanly exited

Contributors

• Author: Remy Sharp
• All contributors

License

MIT / http://jsbin.mit-license.org