Upon gathering my data from Weather Underground, I had written a
simple script calling each piece of data thinking that is all I would need. I
was wrong, however, and the reason is due to JavaScript's advantage as well as
its disadvantage as a programming language.
JavaScript
executes programs in an asynchronous fashion, which is unusual to a Ruby
programmer like me. What's the difference? A synchronous program is executed
line by line and whenever a defined function is called, the computer waits
until the function has completed its work to move execute the remaining code.
Asynchronous languages execute code whether or not a function has completed its
work or not. This is a little confusing, but it is one the main reasons
JavaScript is so popular: its quick. So why would this cause programming
problems?
If I were to
simply assign the "$.getJSON" call to a variable and log it to
the console, it would return the JSON history, but not be accessible. Due to
the asynchronous nature of JavaScript, the function executes after the JSON
data is no longer available. However, JavaScript has a unique property that is
both unusual, but also extremely useful: passing functions into functions. In
order to retain the data from the API call we have to assign the data to a
function and app it into other functions that use the data for our purposes. Imagine
if you will that you have predefined functions and you’re essentially calling
back to them throughout your script. This is called a callback and it is quite confusing
but also quick. Here’s an idea of what a callback looks like in my script:
function testIdea(value){
console.log(value);
var apiCall =
"https://api.wunderground.com/api/f946ee8192f9f7ca/conditions/q/" +
value.location.state + "/" + value.location.city + ".json";
callData(apiCall);
}
var geoLocate =
$.getJSON("https://api.wunderground.com/api/f946ee8192f9f7ca/geolookup/q/autoip.json",
function(api) {
testIdea(api);
})
This tends to be very confusing, but not too bad once you
get the hang of it. However, this outlines one of the disadvantages JavaScript
has for large scale apps versus another backend language like Java. Imagine
having different sets of callbacks for multiple types of information. The
script will get quite confusing. However, now my scripts are set up and all I
have to do it make my site pretty and add some minor functionality. The hard
work is over and its nothing but sunny skies ahead!
