element-ref.md

Element ref - #

In the last chapter, we ended with our input component able to display and change the title of our todo item. input.component.ts should look like this:

{% code-tabs %} {% code-tabs-item title="src/app/input-button-unit/input-button-unit.component.ts" %}

import { Component, OnInit } from '@angular/core';

@Component({
  selector: 'app-input-button-unit',
  template: `
    <p>
      input-button-unit works!
      The title is: {{ title }}
    </p>

    <input [value]="title"
           (keyup.enter)="changeTitle($event.target.value)">

    <button (click)="changeTitle('Button Clicked!')">
      Save
    </button>
  `,  
  styleUrls: ['./input-button-unit.component.css']  
})    
export class InputButtonUnitComponent implements OnInit {
  title = 'Hello World';

  constructor() { }                     

  ngOnInit() {
  }

  changeTitle(newTitle: string) {
    this.title = newTitle;
  }
}

{% endcode-tabs-item %} {% endcode-tabs %}

First let's remove a bit of the template that we don't need. Remove these lines:

{% code-tabs %} {% code-tabs-item title="remove this from src/app/input-button-unit/input-button-unit.component.ts" %}

<p>
  input-button-unit works!
  The title is: {{ title }}
</p>

{% endcode-tabs-item %} {% endcode-tabs %}

Now we want to take the value of the input (that the user typed) and change the title when we press the Save button.

We already know how to create a button and react to clicking on it. We now need to pass to the method some data from a different element. We want to use the input element's value from inside the button element.

Angular helps us do exactly that. We can store a reference to the element we want in a variable with the name we choose, for example inputElementRef, using a simple syntax - a hash. Add #inputElementRef to the input element, and use it in the click event of the button:

{% code-tabs %} {% code-tabs-item title="src/app/input-button-unit/input-button-unit.component.ts" %}

template: `
  <input #inputElementRef
         [value]="title"
         (keyup.enter)="changeTitle($event.target.value)">

  <button (click)="changeTitle(inputElementRef.value)">
    Save
  </button>
`,

{% endcode-tabs-item %} {% endcode-tabs %}

Now we can use the value that the user entered in the input element in the method called when clicking the Save button!

What is that # we see?

Angular lets us define a new local variable named inputElementRef (or any name you choose) that holds a reference to the element we defined it on, and then use it any way we want. In our case, we use it to access the value property of the input.

Instead of hunting down the elements via a DOM query (which is bad practice, as we discussed), we now can put element references in the template and access each element we want declaratively.

Next, we'll build the list of todo items.

Explore the element reference

Just like we did in the previous chapter, when we logged $event, you can do the same with #inputElementRef.

Playground: Change the method changeTitle so it will receive the whole element reference and log it to the console:

{% code-tabs %} {% code-tabs-item title="src/app/input-button-unit/input-button-unit.component.ts" %}

<input #inputElementRef
       [value]="title"              
       (keyup.enter)="changeTitle(inputElementRef)">

<button (click)="changeTitle(inputElementRef)">
  Save
</button>

{% endcode-tabs-item %} {% endcode-tabs %}

changeTitle(inputElementReference) {
  console.log(inputElementReference);
  this.title = inputElementReference.value;
}

Don't forget to put the code back the way it was after you're finished experimenting! It's best to pass to a method exactly the value it needs, instead of the whole object.

Resources

Angular Template Reference Variables