I am capturing MatSelectChange events from a dynamic forms library in my .ts file. This works just fine, but when I capture the event, I don't know how to acquire the previously selected value.
Getting the current value is easy, I am surprised that the prior value isn't immediately available for access.
The event contains access to $event.value and $event.source.
I have tried to dig deep into the source member, but I can't find the previous value there either as it is just the current select control.
There is no way to get it from the event unfortunately. You will have to store it in a component variable, and read it from there. Which shouldn't add that much overhead, because most of the time you would have to do that anyways:
export class SelectOverviewExample {
selected?: string;
onChange(event: MatSelectChange): void {
console.log('Old value', this.selected);
this.selected = event.value;
console.log('New value', event.value);
}
}