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:

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<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>