feat(runtime): v5 batched componentShouldUpdate

[johnjenkins]

What is the current behavior?

GitHub Issue Number: #6759

What is the new behavior?

Documentation

Does this introduce a breaking change?

• Yes
• No

componentShouldUpdate now fires once per render cycle instead of once per changed @Prop/@State. The callback signature changed from (newVal, oldVal, propName) to a single changes argument: a map of every prop/state name that changed since the last render to its { newVal, oldVal }.

@Prop() prop1;

componentShouldUpdate(changes) {
  if (changes['prop1'].newVal === changes['prop1'].oldVal) {
    return false;
  }
}

Alternatively, you can get some typing via ComponentShouldUpdateChanges

@Prop() prop1;

componentShouldUpdate(changes: ComponentShouldUpdateChanges<this>) {
  if (changes['unknown'].newVal === changes['unknown'].oldVal) { // << will throw
    return false;
  }
}

Migration pathway

Users should update their componentShouldUpdate method to accept the single changes argument (optionally typed as ComponentShouldUpdateChanges<this> for per-prop typing) and 2) rewrite any per-prop branching logic to key off changes[propName] instead of the old propName parameter.

Additionally, a compiler warning will throw when more than one argument is passed to componentShouldUpdate

Testing

Other information