Passing Parameters to an Angular2 Component

One of the greatest advantages of using components is reusability, which means once you’ve create your component you can use it in several places across your project without having to recreate it everytime. But for that to be possible we have to be able to pass parameters to our components, that’s what I’ll be showing you in this tutorial.

Some time ago I’ve written a tutorial on how to create an autocomplete, but I didn’t show how to pass the data as a parameter, it was hardcoded in the component, so if I had to use it somewhere else with other data I would have to rewrite everything. Of course nobody wants that, so let’s see how we can make it better.

This is the component we have so far (I’ve omitted some code to make it easier to read):

import {Component, ElementRef, Input} from 'angular2/core';
 
@Component({
    selector: 'autocomplete',
    template: `
        //template here
    	`
})
export class AutocompleteComponent {
    public countries = [ "Albania","Andorra","Armenia","Austria","Azerbaijan","Belarus","Belgium","Bosnia & Herzegovina",
                        "Bulgaria","Croatia","Cyprus","Czech Republic","Denmark","Estonia","Finland","France","Georgia",
                        "Germany","Greece","Hungary","Iceland","Ireland","Italy","Kosovo","Latvia","Liechtenstein",
                        "Lithuania","Luxembourg","Macedonia","Malta","Moldova","Monaco","Montenegro","Netherlands",
                        "Norway","Poland","Portugal","Romania","Russia","San Marino","Serbia","Slovakia",
                        "Slovenia","Spain","Sweden","Switzerland","Turkey","Ukraine","United Kingdom","Vatican City"];
    ...
}

What we have to do here is to remove this array of countries and replace it with a variable annotated with the @Input decorator from angular2/core. After the modification the component should look like this:

export class AutocompleteComponent {
    @Input() data;
    ...
}

The @Input() decorator makes the data variable a data-bound property, now this variable can receive data passed from a parent component.

Now let’s create a parent component that uses our autocomplete:

import {Component} from 'angular2/core';
import {AutocompleteComponent} from './autocomplete.component';
 
@Component({
    selector: 'my-app',
    directives:[AutocompleteComponent]
    template: `
            <autocomplete [data]=countries ></autocomplete>
    	`
})
export class AppComponent {
    public countries = [ "Albania","Andorra","Armenia","Austria","Azerbaijan","Belarus","Belgium","Bosnia & Herzegovina",
                        "Bulgaria","Croatia","Cyprus","Czech Republic","Denmark","Estonia","Finland","France","Georgia",
                        "Germany","Greece","Hungary","Iceland","Ireland","Italy","Kosovo","Latvia","Liechtenstein",
                        "Lithuania","Luxembourg","Macedonia","Malta","Moldova","Monaco","Montenegro","Netherlands",
                        "Norway","Poland","Portugal","Romania","Russia","San Marino","Serbia","Slovakia",
                        "Slovenia","Spain","Sweden","Switzerland","Turkey","Ukraine","United Kingdom","Vatican City"];
 
}

As you can see, I’ve just copied the data from the other component to this one. If you take a look at the autocomplete in the template you’ll see that it has the attribute [data]=countries, this is how I’m assigning the countries list to that variable with the @Input decorator I’ve create before. If you run your project you’ll see that it’s working the same way as before, but now you can create more autocompletes passing different datasets.

Hope this tutorial was helpful, just leave a comment if you have any doubts.

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