function invariant(condition, format, a, b, c, d, e, f) {
	  validateFormat(format);

	  if (!condition) {
	    var error;
	    if (format === undefined) {
	      error = new Error('Minified exception occurred; use the non-minified dev environment ' + 'for the full error message and additional helpful warnings.');
	    } else {
	      var args = [a, b, c, d, e, f];
	      var argIndex = 0;
	      error = new Error(format.replace(/%s/g, function () {
	        return args[argIndex++];
	      }));
	      error.name = 'Invariant Violation';
	    }

	    error.framesToPop = 1; // we don't care about invariant's own frame
	    throw error;
	  }
	}
Use invariant() to assert state which your program assumes to be true.

Provide sprintf-style format (only %s is supported) and arguments
to provide information about what broke and what you were
expecting.

The invariant message will be stripped in production, but the invariant
will remain to ensure logic does not differ in production.