JavaScript Assertion

assert.js

// debugging technique
// via: http://www.learncomputer.com/javascript-tricks-you-may-not-know/

function AssertException( msg ) {
  this.msg = msg;
}

AssertException.prototype.toString = function() {
  return 'AssertException: ' + this.msg;
}

function assert( exp, msg ) {
  if ( !exp ) {
    throw new AssertException( msg );
  }
}

// usage
// if first param evaluates to false then exception is thrown w/ 2nd param as message

try {
  assert( obj != null, 'Object is null' );
} catch( err ) {
  if ( err instanceof AssertException ) {
    // error handling
  }
}