Waiting for Condition Script in ServiceNow

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Sometimes as a ServiceNow developer you perform some kind of action in your code which triggers a Business Rule (or another asynchronous process) and you want to wait around for the result.

How do you do this?

ServiceNow's JavaScript engine, Rhino, doesn't support setTimeout and it runs on ES5 so it doesn't support Promises or async/await.

There's gs.sleep() which is an out-of-the-box method which blocks the current execution context, but it doesn't work in global scope.

You can write your own sleep / wait function using something like this:

var waitForSeconds = 10;
var endSleep = new GlideDateTime().getNumericValue() + waitForSeconds * 1000;
while (new GlideDateTime().getNumericValue() < endSleep) {
    // intentionally wait
}

If you want to also check for a condition, you can do something like this:

var waitForCondition = function (func, timeout) {
	var startTime = new GlideDateTime().getNumericValue();
	var endTime = startTime + timeout * 1000; // convert timeout to milliseconds
 
	while (new GlideDateTime().getNumericValue() < endTime) {
		var result = func();
 
		// If the condition is met, we're done!
		if (result) {
			return true;
		}
 
		// Sleep for 1 second before checking again
		var endSleep = new GlideDateTime().getNumericValue() + 1000;
		while (new GlideDateTime().getNumericValue() < endSleep) {
			// intentionally wait
		}
	}
 
	// Condition not met within timeout
	return false;
};

This function takes in a condition function, which evaluates a condition, as well as a timeout in seconds. It will check the condition every second until the condition is met or the timeout is reached.

And you can use it as follows:

var openIncidentsExist = function () {
    var grIncident = new GlideRecord('incident');
    grIncident.addQuery('status', '1');
    grIncident.query();
 
    return grIncident.hasNext();
};
 
waitForCondition(checkForOpenIncidents, 10);
// Returns false if no open incidents exist after 10 seconds
// Returns true if open incidents exist within 10 seconds