Promise Throttle

Implement createThrottle(interval) that ensures a minimum gap of interval ms between starting each async task.

Requirements

• add(asyncFn) — schedule an async function. Returns a promise that resolves with the function's result.
• Tasks start in the order they are added.
• At least interval ms must elapse between the start of consecutive tasks.
• Tasks may overlap in execution (this is not a concurrency limit).

Example

const throttle = createThrottle(100);
throttle.add(async () => 'a'); // starts at t=0
throttle.add(async () => 'b'); // starts at t=100
throttle.add(async () => 'c'); // starts at t=200