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: 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. 
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  • 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.
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  • 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.
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