Windows® 8.1 Apps with HTML5 and JavaScript Unleashed

Creating Promises

If your app has a function that takes more then a few milliseconds to complete then you should return a promise so that your app can continue to work while the function is completing. You can create your own promises by creating a new instance of the Promise class. The constructor for the Promise class requires a function that accepts three parameters: a complete, error, and progress function parameter.

For example, the code in Listing 2.10 illustrates how you can create a method named wait10Seconds() which returns a promise. The progress function is called every second and the complete function is not called until 10 seconds have passed.

LISTING 2.10 Creating a Promise (promiseCreate\promiseCreate.html)

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