Monitoring

The Elapsed module has a few functions for tracking passage of time.

An overview:

• Elapsed.since(): time from a start point
• Elapsed.interval(): time from start point, and between each subsequent call
• Elapsed.once(): one-time measurement from a start point

Elapsed

Since

since yields how much time (in milliseconds) has passed since first invoked. This is the fixed reference point all later invocations are compared to.

// repl-pad
import { Elapsed } from "https://unpkg.com/ixfx/dist/flow.js"

// A. Start monitoring elapsed time
const elapsed = Elapsed.since();

// ...some time later ...

elapsed(); // B. Elapsed time since (A)
// ...some time later ...
elapsed(); // C. Elapsed time since (A)

Each call to elapsed() reports the current time, it will continually change.

Interval

Elapsed.interval reports the time from the first initialisation and each subsequent call. Unlike since, there is a not a fixed reference point. It is always comparing to either the initial time or when the callback was last run.

// repl-pad
import { Elapsed } from "https://unpkg.com/ixfx/dist/flow.js"

// A. Start monitoring elapsed time
const elapsed = Elapsed.interval();

// ...some time later ...

elapsed(); // B. Elapsed time since (A)
// ...some time later ...
elapsed(); // C. Elapsed time since (B)

Once

Elapsed.once fixes both the start point and a second reference time. After initialisation, it records the time at which the first call happens. This is then given as the value for all future calls.

// repl-pad
import { Elapsed } from "https://unpkg.com/ixfx/dist/flow.js"

// A. Start monitoring elapsed time
const elapsed = Elapsed.once();
// ...some time later...
elapsed(); // B. Time since (A). Since it is the first call, we now fix the second reference.
// ...some time later...
elapsed(); // C. Will be same value as earlier (B-A)
elapsed(); // D. As above, forever

Human-friendly elapsed time

toString prints elapsed time in a human-friendly way:

// repl-pad
import { Elapsed } from "https://unpkg.com/ixfx/dist/flow.js"

// With .since()
const elapsed = Elapsed.since();
Elapsed.toString(elapsed); // if it gets a function, it calls it

// With regular millis
const startTime = Date.now();
Elapsed.toString(Date.now() - startTime);

Completion

If you have a known time period and you want to track reaching that elapsed time, use Elapsed.progress. It gives a clamped percentage (0..1) for completion.

// repl-pad
import { Elapsed } from "https://unpkg.com/ixfx/dist/flow.js"

// Start tracking 1 second time duration
const timer = Elapsed.progress(1000);

// ...later, call timer() to get a 0..1 value for completion:
timer(); // Yields 0..1

Intervals can be used:

// Track progress towards 4 minutes
const timer = Elapsed.progress({ mins: 4 });