WebPages JavaScript Promises

In JavaScript, the Promise notation is used in computation of asynchronous functions. A Promise can be in three states: pending, fulfilled or rejected. It can take two arguments: a results handler and an error handler either will be called only once and will return a value after the asynchronous function has finished. This allows for chaining multiple calls which will execute sequentially. It is also required when the result of a function is needed, for example when assigning the result to a variable as in the example below.

Example: When assigning the result of an asynchronous function to a variable, use the .then() syntax:

$System.GetUptimeMilliseconds().then(function(result){$mytime_test = result});

Instead of:

$mytime_test = $System.GetUptimeMilliseconds();

Example: Error cases can also be handled by specifying a second argument with a callback function:

asyncCallToDesigner(parameters).then(function(result) {
	//handle result here	
},
function(error) {
	//handle error here	
});

Note:

When handling error callbacks, a JavaScript error object will be passed. For more information, see the Error topic (requires Internet access).
The then callback is not required; it is only needed to handle the result of an asynchronous call. In addition, within the then, error handling is not mandatory.
The parameter names in the function callbacks can be arbitrary names, not just result or error. Parameters are not mandatory; you can run a function, instead.