Detect if data in an Angular form (not reactive) was changed
You can check the dirty flag, which tells you if the form is dirty or not.
<button type="submit" [disabled]="!form.dirty">Save</button>The form becomes dirty if you change some value in it.
Check here for more details: https://angular.io/guide/forms
According to your comment 'But what if i erase 1 symbol in input and then wright it again (the value is the same, but form was changed)?' I suggest this solution.
The general idea is to store the initial value of the form as separate object (just cloning it). And then create a boolean function which simply iterate through the key-values and compare Updated data with the Initial data. After this just bind the result of this function to your submit button [disabled]="yourCheckMethod(form.value)".
You can try it with the pristine property like this:
<button type="submit" [disabled]="form.pristine">Save</button>This property checks if your form has changed since it was loaded.