Advanced promises

In this section, we'll explore two more ways to use promises. We'll create functions that take input and return a promise. Also, we'll explore promise chaining, which will let us combine multiple promises.

Providing input to promises

Now the problem with the example we discussed in the previous section is that we have a promise function, but it doesn't take any input. This most likely is never going to be the case when we're using real-world promises. We'll want to provide some input, such as the ID of a user to fetch from the database, a URL to request, or a partial URL, for example, just the address component.

In order to do this, we'll have to create a function. For this example, we'll make a variable, which will be a function called asyncAdd:

var asyncAdd = () => {

}

This will be a function that simulates the async functionality using setTimeout. In reality, it's just going to add two numbers together. However, it will illustrate exactly what we need to do, later in...