combine (combineLatest)

Combines multiple observables into a single observable that emits an array of their latest values. Emits whenever any of the source observables emit, but only after all sources have emitted at least once.

Marble Diagram

combine

Example

//  Timeline:
//
//  name$     "Alice"                 "Bob"
//  age$                25                        30
//  user$               ["Alice",25]  ["Bob",25]  ["Bob",30]
//
//  Explanation:
//  - combine waits for all sources to emit at least once
//  - Then emits the latest value from all sources whenever any source emits
//  - Always emits an array with the latest values from each source

const name$ = source<string>();

const age$ = source<number>();

const user$ = combine([name$, age$]);

const userHistory: (readonly [string, number])[] = [];

user$.subscribe(([name_, age]) => {
    userHistory.push([name_, age]);
});

name$.next('Alice'); // nothing logged (age$ hasn't emitted yet)

assert.deepStrictEqual(userHistory, []);

age$.next(25); // logs: { name: 'Alice', age: 25 }

assert.deepStrictEqual(userHistory, [['Alice', 25]]);

name$.next('Bob'); // logs: { name: 'Bob', age: 25 }

assert.deepStrictEqual(userHistory, [
    ['Alice', 25],
    ['Bob', 25],
]);

age$.next(30); // logs: { name: 'Bob', age: 30 }

assert.deepStrictEqual(userHistory, [
    ['Alice', 25],
    ['Bob', 25],
    ['Bob', 30],
]);

View source on GitHub