Angular Snippets

Signal Reactivity Cheat sheet

angular16 signal reactivity

Until now, Angular used Zone JS to perform change detection and therefore to refresh the view.

Change detection works by detecting common browser events like mouse clicks, HTTP requests, and other types of events, and deciding if the view of each component needs to be updated or not. By default, Angular uses the ChangeDetectionStrategy.Default change detection strategy which checks every component in the component tree from the top to the bottom every time a common browser event is emitted. This way of checking don’t take into account the components’ dependencies and is called dirty checking. This can negatively influence your application performance specially for large application with many components.

With the release of Angular version 16, a new system of primitive reactivity will be created: Signal Reactivity which don’t need zone js to trigger a refresh of a view.

The goal of this snippet is to give you a cheat sheet about signal reactivity and give you keys to be ready to work with them.

Create a signal

Create a signal is very easy, it’s just calling a function

const counter = signal(0); // create a signal with initial value to 0;

Equality Function

By default, signal() uses a default ValueEqualityFn.

  • For primitive values, is utilized
  • For reference values (object and array), they are always considered unequal

We can also provide a custom ValueEqualityFn to signal() for custom compare logic on Signal’s update

const users = signal<User[]>([], (a, b) => userCompareFn(a, b));

Update a signal

The signal function return a SettableSignal. This gives you some amazing possibilities

const todos = signal([]);

todos.set(["Make My dinner"]); // directly set the signal to a new value and notify all the dependents

todos.update((currentTodos) => [
  "Create a new Angular Snippet",
]); // update the value of the signal based on its current value and notify all dependents

// NOTE: `mutate` will by-pass equality check and will always notify change
todos.mutate((currentTodos) => {
  currentTodos.push("Participate to Open Source");
}); // update the currentValue by mutating it in-place and notify all the dependents

Get the value of a signal

The way to get the value of a signal will be the same in the template as in the component.

const counter = signal(0); // create a signal with initial value
console.log(counter()); // print the value of the signal which is 0


computed() creates a memoizing signal, which calculates its value from the values of some number of input signals.

const person = signal<{ firstname: string; lastname: string }>({
  firstname: "John",
  lastname: "Doe",

// Automatically updates when person() change;
const presentation = computed(() => {
  const fullName = `${person().firstname} ${person().lastname}`;
  return fullName;

person.update((person) => ({ firstname: "Angular", lastname: "Snippet" }));


effect() schedules and runs a side-effectful function inside a reactive context. Signal dependencies of this function are captured, and the side effect is re-executed whenever any of its dependencies produces a new value.

const idTodo = signal(12);

  () =>
      .then((response) => response.json())
      .then(console.log) // will sent the request with idTodo() = 12
Back to snippets