97. Using the Renderer to build a Better Attribute Directive

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In the last lecture,

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we created our first basic directive.

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And it's doing its job,

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we learned how to create a selector,

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how to use that selector,

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like an attribute in this case,

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since we set up an attribute selector,

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and how to register it in AppModule.

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We also learned how to get access to the element the directive sits on.

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This,

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however, is not the best way of changing that style.

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Because,

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as you might recall from some earlier lecture in this course,

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accessing elements directly like this is not a good practice.

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You should use a different tool,

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which I'll show you in a second,

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because Angular actually is also able to render

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your templates without a DOM,

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and then these properties might not be available.

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It could do this when using service workers,

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so basically some advanced use cases,

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but nonetheless,

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it's not a good practice to directly access your elements.

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How should you access them then?

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Well, there is some other helper you can inject.

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It's the renderer.

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So let's do this.

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But actually,

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let's not do it in our basic highlight directive.

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Let's create a new one.

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And for this,

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I will create a new one with the generate command or just G

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as you learned with the CLI and then directive or

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just D and then any name of your choice.

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And I'll name this better highlight.

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So this will give us a new file or two new files.

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I can delete the testing file.

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And we can also put this into its own folder,

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of course.

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It's not the default,

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but let's do it here.

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Better highlight.

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You could also create a central shared or directives folder

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where you store all your directives.

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For now,

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just for demo purposes and to have a clear separation and make this easy

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to see, I'll put them into individual folders.

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So better highlight directive here.

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in the app module i will need to adjust my path since i just moved it

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to the better highlight folder

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so make sure to point to the right path in the right file then in

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there we got a selector app better highlight now inject

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let's inject this better tool i was referring to it's

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the renderer which is of type renderer

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2.

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And this needs to be imported from at Angular slash core.

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Now with this injected,

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we can use it and I will use ngOnInit again to still stick

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to this best practice of doing initialization work there.

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Make sure to import ngOnInit or just onInit here from

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at AngularCore.

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And now let's implement ngOnInit here.

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And there I can now use the renderer.

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I do this by calling the property,

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which I created here,

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private renderer.

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And there we get a couple of helper methods you can use to work with

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the DOM basically.

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Now, one important method I'm interested in here is the setStyle

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method. This method allows us to,

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guess what,

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set the style of some element.

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Now,

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the problem here is for that,

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we need to have the element for which we want to set the style.

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And of course,

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in Angular, there are different ways of getting such an element.

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Here in the directive,

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it's exceptionally simple.

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We already saw how to get one in the basic directive,

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the basic highlight directive.

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We can simply inject the element reference.

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So I'll add another private property here or argument,

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which will automatically be bound to a private property,

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I should say, which I'll name LREF.

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And this will be of type element ref,

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which we then also,

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as before,

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need to import here,

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element ref from at Angular core.

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Now, with this import added here,

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now I can use this element ref here by calling this lref.

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And here I then want to access the native element.

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And that's important.

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We can't pass the reference itself.

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We need to get access to the underlying element and pass this as a first argument here to

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setStyle.

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Now setStyle takes a couple of other arguments.

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We defined which element we want to style.

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Now we have to define which style we want to set.

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And that would be the background color in our case.

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With the style property defined,

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the third argument we pass to the setStyle method is the value we want to assign

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for this property.

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Now we could set the background color here to blue.

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The fourth and final argument is a flags object.

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Here we can set a couple of flags for this style.

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And this is optional.

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I will leave it out here.

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What you could set here are things like if you want to add an important

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tag,

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so this...

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exclamation mark important annotation for a style to overwrite other styles or

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something like that now this however does it for my cases

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here and now if we save this with our better the highlight

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directive already added to app module we can go to the app component and

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add it here too

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I will simply duplicate this paragraph here and use app better

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highlight here,

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our new directive,

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again,

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which is available through the selector since we also added it to the

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app module.

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And then here I want to style this with a better directive.

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Now, if we save this and let it recompile and reload the browser,

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we already see the blue background here behind

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this paragraph.

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So our new directive here,

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the better directive is working.

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And now we're using the renderer,

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which is a better approach of accessing the DOM.

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Now,

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why is it a better approach?

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Angular is not limited to running

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in the browser here.

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It, for example,

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S… Speaker 1 (97. Using the Renderer to build a Better Attribute Directive)

also works with service workers.

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And these are environments where you might not have access to the DOM.

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So if you try to change the DOM as you did here in basic

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highlight by directly accessing the native element and the style of this element,

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you might get an error in some circumstances.

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Now, to be honest,

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in most circumstances,

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you probably don't.

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And you probably also know if your app is going to run in the browser

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or not.

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Still, it is a better practice to use the renderer for DOM access

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and to use the methods the renderer provides to access the DOM.

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You can learn more about the renderer in an article after this lecture

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here if you're interested.

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Just another note,

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I had to rerecord this part here because the renderer

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type here changed from renderer v2 to just renderer 2,

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as did some arguments you could pass to set style.

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Therefore,

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in the other videos in this section,

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you will see that this code looks slightly different.

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Not by much,

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though.

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Don't get confused by this.

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The code you see here is the code you should use and the code which will work.

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All the other code shown in the section,

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of course, is not changed,

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is still the same.

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It's only this renderer set style method and the renderer type,

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which is now renderer2 and not renderer v2,

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as you will see in the other videos.

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With that,

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let's move on.

97. Using the Renderer to build a Better Attribute Directive

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