Service Workers and Their Role in Apps

Service Workers and Their Role in Apps

• 1.
  S E RV I C E W O R K E R S w i t h S a l l y a n d L a r r y
• 2.
  Hi Larry! Let'slearn a little about service workers today. Service Workers... Do they do something with building apps?
• 3.
  That means wecan access the app when we don't have signal? Exactly! Service workers make working offline possible. Yes!
• 4.
  It's a JavaScriptfile? Does that mean it works with the DOM? Service Workers are just another JavaScript file that we create. No - and that's what makes it work offline.
• 5.
  Really? How doesthe service worker work with the browser? Even though service workers don't have access to the DOM it does have access to the browser capabilities I'm glad you asked - it's really interesting!
• 6.
  Yes, that's right. Whenyou go to a website you either type it in or click on a link, right? Okay, after you type or click on the URL your computer uses the cables and satellites to contact the web server that's hosting your website. The information you're looking for is then sent to you on those cables and satellites from the web server.
• 7.
  Search for www.hocking.edu Sees thehomepage for www.hocking.edu For example, if Susie is looking to check out Hocking College she can do a search online and click on the link for www.hocking.edu. Susie's computer uses cables, radio towers and satellites to find the server where the Hocking College website is hosted. The server sends her the files (the web pages) she's asked for.
• 8.
  If a ServiceWorker file is included, Susie's search goes to the Service Worker first. Search for www.hocking.edu Sees the homepage for www.hocking.edu
• 9.
  Well, the service workerleaves instructions to the browser that Susie is using. Those instructions will be performed before the request is sent further. Do you see how Susie's request went to a service worker instead of going straight to the radio towers, cables and satellites? Yes, what does it do there?
• 10.
  Yes! That's whythese service worker pages don't access the DOM. If no other pages are loaded yet, there's nothing for it to look through. For example, the service worker can tell the browser "If the user is asking for a particular URL, run this JavaScript file (the service worker file) first." So the browser runs that file first before any of the other pages are searched for or loaded?
• 11.
  There are threedifferent analogies we can use to help better understand. Let's go over them. Cookie Virus Toolbox Cookies and Service Workers are downloaded when accessing a website Service Workers are more powerful than cookies as they contain a set of instructions. Those instructions are reviewed before making a requests to the website that originally installed the service worker. Viruses and Service Workers are installed in the background when first visit a website. Afterwards when a request to the website is made, the service worker intercepts it. The service worker can only handle requests for the original website that installed the service worker. Tools and Service Workers don't do much on their own but they are useful when needing to access something. Service workers allow access to powerful browser features Instructions can be written in service workers to take advantage of the tools
• 12.
  Yes! You gotit! You can see that all three analogies help with the understanding of what a service worker does. Yes, so basically the service worker JavaScript file is downloaded onto our computer when we first visit a website. The next time we visit our browser reads those instructions first. Does that sound right?
• 13.
  So you cansee that service workers can be very powerful. But you know what they say "With great power, comes great responsibility". Yeah, I think I've heard that before. Think about it. If there was a hacker who wanted to create havoc all they would have to do is impersonate a website and write their own service worker with evil instructions. So there are some policies that need to be followed.
• 14.
  It's important tobe sure that the service worker really belongs to the site it claims it's from. For example if a service worker says its for www.example.com - it really is from www.example.com Okay, I think I know what you mean. Can you explain a bit more? Certainly! Sometimes webpages use third party providers to hold images and other assets. That works fine for those instances. The service workers HAVE to be part of the original website. It can't be hosted elsewhere.
• 15.
  The same originis one policy that service workers have to follow. Okay, what is the other one? Service workers can only be used on HTTPS websites. If a website is only HTTP and doesn't have the S (indicates it's secured), the service worker won't work.
• 16.
  When publishing yourwebsite for others to see you need to be sure your site is secured with HTTPS, but you don't need to do that while your still building your app. That's good! I wasn't sure how that was going to work when we're still in testing phase. How else can we see our site with the service worker in action? You can build and test with the service worker while working with your local host (web server on your own computer).
• 17.
  Hopefully this helpsexplain what a Service Worker is and how it help build apps for users to use - even if they aren't online or connected. If you have questions please feel free to reach out to Tasha Penwell at Hocking College at the information below. Text: 740-300-1684 Email: penwellt31810@hocking.edu Source: https://abookapart.com/