Conditionally make input field readonly in Angular 2 or 4: Advice + Best/which way to do it

Question

I was attempting to answer someone elses question. And in doing so realised there was quite a bit of uncertainty in my mind about a few things. I'm hoping someone can provide feedback on the numbered points 1..4:

Task: Conditionally make input field readonly

Relevant section of HTML:

<input type="text" placeholder="Club Name" #clubName>

Add this to Typescript component.

// class properties
@ViewChild('clubName')
inp:HTMLInputElement; // Could also use interface Element

// conditionally set in some other methods of class
inp.setAttribute('readonly', 'readonly');
inp.removeAttribute('readonly');

Have to say this is a grey area for me.

1. Is referencing HTMLInputElement or Element directly with @ViewChild in Angular 2+ a bad practice? Only, I've often seen examples using ElementRef or chaining off to nativeElement from ElementRef.

Since VS Studio doesn't have Intelli-sense for those, I suddenly feel like I'm coding in the dark. i.e, you never get feedback about methods setAttribute or removeAttribute, their parameter requirements etc. (I'm aware of As to cast too)

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2. Then, after looking at the docs, I suspect you can do this directly on your input in the HTML template:

---

<input [attr.readonly]= "isReadOnly">

IIRC I think you have to do this way with a property get in Typescript:

get isReadOnly() :boolean {
}

Is this way valid?

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3. I'm wondering, can you do the method syntax too in the HTML template:

---

<input [attr.readonly]= "isReadOnly()">

Typescript

isReadOnly() :boolean {
}

Is this way valid?

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4. In summary, what's the best approach?

Update: There is also *ngIF so you output one of two input elements with same name. But that sounds to me like a sledgehammer to crack a nut.

Answer 1

You need to use the following (Angular 4):

<input [readonly]="isReadOnly">

If you use att.readonly then the input will always be read-only because the readonly attribute will be present even if its value is false. By using [readonly] Angular will only place the attribute if isReadOnly is true.

In HTML, the following is sufficient to cause an input to be read-only:

<input readonly>

Answer 2

None of them worked for me.. Finally found solution by creating custom directive angular.. Directives are powerful feature of angular

1. Create Custom Directive

@Directive({
  selector: '[readonly],[readOnly]',
  host: {
    '[attr.readonly]': '_isReadonly ? "" : null'
  }
})
class ReadonlyDirective {
  _isReadonly = false;

  @Input() set readonly (v) {
     this._isReadonly = coerceBooleanProperty(v);
  };

  ngOnChanges(changes) {
    console.log(changes);
  }
}

2. Add into module declarations

@NgModule({
  ...
  declarations: [ ..., ReadonlyDirective ],
  ...
})

3. Now its time to use directive as following.

<input [(ngModel)]="name" [readonly]="isReadonly" />
or
<input [(ngModel)]="name" readonly />

Directives are powerful feature of angular, I strongly recommend you to go through https://angular.io/guide/attribute-directives

Demo https://stackblitz.com/edit/angular-readonly-input-aifncy?file=src/app/app.component.ts

Answer 3

All depends on what you want to achieve. At first look, I would say that pct. 2 is the simplest way to do it:

<input [attr.readonly]= "isReadOnly">

Then, on your component you declare the variable:

isReadOnly: boolean;

After, you assign the value as you wish:

// when you want to be read-only
isReadOnly = true;
// whe you want to be editable
isReadOnly = false;

Answer 4

You can use <input readonly="{{ variable }}>".

In your *.component.ts, initialize the variable:

private variable: boolean = true;