What is updateValueAndValidity

Question

These docs state the following:

If emitEvent is true, this change will cause a valueChanges event on the FormControl to be emitted. This defaults to

Answer 1

The sourcecode can be helpful to clear up exactly what it's doing:

https://github.com/angular/angular/blob/master/packages/forms/src/model.ts

Currently it seems to be doing the following (this list is based on method names):

• 'Set initial status' - which makes .status 'VALID' except if ALL controls are disabled, in which case it makes it 'DISABLED'
• 'Updates value' - this seems to set .value if the control is enabled, or clear it if disabled.
• 'Runs validator' - this updates the whole error object. So custom errors would be cleared if you'd set any.
• 'Cancel subscriptions' - stops any async validators running at the time
• 'Emit' event - (if emitEvent != false in options). This is just the value and status normal form events.
• Updates parent with same rules - unless onlySelf is set.

Note: it doesn't go down the tree, only up.

I wish they'd put something like this in the docs. They currently say 'Recalculates the value and validation status of the control.' which isn't particularly helpful.