change a variable value using *ngIf in angular 7 - html

Question

I am trying to add some validation using [pattern] in an angular 7 application. I want to disable a button using a variable this.isSubmitDisabled if the pattern has errors ( phoneNumber.errors?.pattern ).
I know that this can be achieved using Reactive form but unfortunately, I cannot use forms. Is there a way to set the variable value to 'true' if phoneNumber.errors?.pattern is true?.
Here is my code:
<input
type="text"
class="form-control"
(ngModelChange)="dialInDetailsChange($event)"
name="dialInDetails"
[disabled]="false"
id="dialInDetails"
pattern="^\d+(?:[,.]\d+)?$"
required
[(ngModel)]="agendaMeeting.dialInDetails"
ngModel #dialInDetails="ngModel" />

Answer 1

You can also check it using .match() in your .ts file. On model change just check whether the entered value matches your regex. If matches then set inputDisabled to false otherwise set inputDisabled to true.
let inputDisabled:boolean = false;
dialInDetailsChange(event:any){
if(agendaMeeting.dialInDetails.match("^\d+(?:[,.]\d+)?$") === null){
inputDisabled = true;
}
else{
inputDisabled = false;
}
}
Edit after recent comment
WORKING DEMO : LINK
myInput='';
result='';
changeHandler(){
if(this.myInput.match('^[\\s]+[a-zA-Z]*') === null){
this.result = "correct input";
}
else{
this.result = "there are spaces at the begining."
}
}

Answer 2

i think you can't assign values using expression in your template, check the documentations
You can't use JavaScript expressions that have or promote side effects, including:
Assignments (=, +=, -=, ...)
Operators such as new, typeof, instanceof, etc.
Chaining expressions with ; or ,
The increment and decrement operators ++ and --
Some of the ES2015+ operators

Answer 3

try this :
<input
type="text"
class="form-control"
(ngModelChange)="updateState(phone)"
name="dialInDetails"
[disabled]="false"
id="dialInDetails"
pattern="^\d+(?:[,.]\d+)?$"
required
[(ngModel)]="agendaMeeting.dialInDetails"
#phone="ngModel" />
<button type="button" [disabled]="isDisabled">Submit</button>
updateState(input){
this.isDisabled = input.errors && input.errors.pattern ? true : false ;
}