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4.3 Attribute Bindings

In this lesson we'll see how to bind a property of a component class to the attribute of an element. This is similar conceptually to property binding, but you can use it to target HTML attributes rather than DOM properties.

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4.3 Attribute Bindings

Hi folks. In this lesson, we're going to see what we need to do when we want to bind to an HTML element attribute rather than a property. Usually we'll use property bindings much more often than attribute bindings, and property bindings should generally be preferred. But in some cases, we have no choice but to bind to an attribute. The most common use case for setting attributes, is when we're using area attributes. Because these are implemented only in HTML and not by the DOM at all, so there are no corresponding area properties, only area attributes. In our example app, at the moment, the game and end components are both hidden. As well as setting the hidden property, we can also set the area hidden attributes. The syntax for attribute bindings is actually very similar to the syntax that we use for property bindings. But let's try to see what happens if we set the area hidden attributes using a property binding. So we've used the same square bracket syntax here, let's go back to the browser and see what happens. So we can see now that our app doesn't even render. Let's take a look in the console. And we can see we've got a big, scary error message here. And it's so big we can't even see all of it. But at the top it tells us that we have template parse errors. And it can't bind to area hidden, since area hidden isn't a known property. That's not happening because we're setting the attributes on a component. We'd get exactly the same message if we tried to set an attribute using a property binding, on a regular HTML element. So to turn this into an attribute binding, we just need to prefix the name of the attribute with A-T-T-R. That tells angular that it's actually an attribute we want to bind to and not a property. Let's go back to the browser once again. And we can see that our page is rendered as before. Let's just open up the console. So we can see that the app game and the app end component still exist, but they're hidden. And we can see that they both have the area hidden attribute set to true, perfect. We should also probably set the same action attribute and hidden property on the start component for when we want to hide that a bit later on. And let's just add the corresponding property in the home components class. This time we'll set it to false. Otherwise we'll see very little on the page at all. So in this lesson we looked at attribute bindings. We saw that they are really similar to property bindings and work in a very similar way. And that they also use the square brackets around the binding targets. But to tell Angular that it's an attribute and not a property, we prefix the name of the attribute with A-T-T-R. Thanks for watching.

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