HTMX + Flask: Modern Python Web Apps, Hold the JavaScript Transcripts
Chapter: Exploring the examples on htmx.org
Lecture: Example: Lazy loading
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The next example that we're gonna explore. It's not one that actually appears in our final application, but it's extremely useful.
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Let me lay out the scenario for you. Imagine I've got a page, trying to render it for the user, right? They make a request, we want to show it to him,
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but maybe it's doing some kind of report, or there is some part of the page that's actually really,
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really slow, and I want to get most of the page shown to them and then
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have this other slower section, like a report or a graph or something along those
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lines. I want that to be generated and delivered to the user as soon as
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possible, but without blocking the original page load, and we also want some kind of indicator
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for what's happening. That would fall under the "Lazy Loading" section. Check this out, that's pretty simple.
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So what we do is we say, this section of the page, this whole section, that's one of those slow pieces.
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What I want to do is I want you htmx, to go to the server and call /graph and when it's done, put it right here.
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But while it's loading, I want you to show this indicator with those bars sort
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of spinning around here. And the trigger is going to be that the page has loaded.
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So just the page was shown and then fill out these missing pieces that are slow. In order for this to work,
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you're going to need a little bit of CSS somewhere, included in the page to basically
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have some of the behaviors that are indicated here happening and down here we have our
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graph and this is the part that was slow, but it doesn't take that long, it's like half a second or a second.
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So what we didn't see is this actually loading because by the time I got down here it was done. But if, notice if I load this page, it's instant,
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but there's like a one second processing of something else. If I scroll down, I can refresh here and show that to you.
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So page is loaded. But now it's thinking on the graph request, input came back or the response came back. Boom,
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here's our report and let's go and look at this. So our initial state was that the page was loaded and this section was here.
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Right, this is what we talked about. But then as the document loaded, was complete,
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I said right, now we've got to fill out the slow pieces, and it went and did a request for GET /graph,
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no parameters. The response was, here is your generated image, of your report. How cool is that? So I'm
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sure there are many websites that there's a little part of it or a little
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piece of information that's slow and the rest is really pretty quick, and yet the user
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experiences, I go there and I click, and I wait, and I wait, and I wait and finally the page loads.
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This would be so much better. Show most of the page, and calculate the little final things that you need using one of these lazy loads.