CODEWITHSUNDEEP
javascriptweb-worker
wordpressm
wordpressm

Reputation: 3267

How multiple scripts run without webworkers?

I am learning web-workers and found that we can run multiple scripts now on web pages. This is quite interesting but one thing again came in to my mind was If we can't run multiple scripts before html web-workers, How did I run several slideshows on a single html page without using above technology. I may not properly understand this concept. Can anyone explain how I ran several slideshows which was designed from only JavaScript without web-workers?

Upvotes: 0

Views: 143

Answers (1)

jfriend00
jfriend00

Reputation: 707248

Slideshows will typically use a setTimeout() to show the next slide. You can simply have multiple slideshows each using their own setTimeout().

The first slideshow shows it's initial image, then sets a setTimeout() for a particular time in the future when it wants to switch to the next slide. The second slideshow then shows it's initial image and set a setTimeout() for a particular time in the future when it wants to switch to the next slide.

Then, both slideshow are done executing for now until one of their setTimeout() fires. They never technically "execute at the same time". Only one ever actually has code running at a time. Using short enough timer intervals, it may appear they are both operating at the same time, but technically they aren't.

Javascript without WebWorkers is single threaded. There is only ever one thread of execution running at a time. Timers are often used to simulate multiple things happening at the same time (such as multiple javascript-based animations running at the same time). But, that is only a simulation (sometimes a very effective one).

Slideshows may also use CSS3 animations or transitions to show slide transitions from one slide to the next which are controlled by the browser and don't use javascript to execute the animations (they use native code which may or may not be multi-threaded or may even use the GPU - that's browser implementation dependent).

You may find this answer and the references it contains helpful in understanding the javascript event model and single threading: How does JavaScript handle AJAX responses in the background?.

Upvotes: 1

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