`Metrics`

A Metrics object lets you define, query, and listen to, aggregations of Cell values within a Table in a Store.

This is useful for counting the number of Row objects in a Table, averaging Cell values, or efficiently performing any arbitrary aggregations.

Create a Metrics object easily with the createMetrics function. From there, you can add new Metric definitions (with the setMetricDefinition method), query their values (with the getMetric method), and add listeners for when they change (with the addMetricListener method).

This module provides a number of predefined and self-explanatory aggregations ('sum', 'avg', 'min', and 'max'), and defaults to counting Row objects when using the setMetricDefinition method. However, far more complex aggregations can be configured with custom functions.

Example

This example shows a very simple lifecycle of a Metrics object: from creation, to adding a definition, getting a Metric, and then registering and removing a listener for it.

import {createMetrics, createStore} from 'tinybase';

const store = createStore().setTable('species', {
  dog: {price: 5},
  cat: {price: 4},
  worm: {price: 1},
});

const metrics = createMetrics(store);
metrics.setMetricDefinition(
  'highestPrice', // metricId
  'species', //      tableId to aggregate
  'max', //          aggregation
  'price', //        cellId to aggregate
);

console.log(metrics.getMetric('highestPrice'));
// -> 5

const listenerId = metrics.addMetricListener('highestPrice', () => {
  console.log(metrics.getMetric('highestPrice'));
});
store.setCell('species', 'horse', 'price', 20);
// -> 20

metrics.delListener(listenerId);
metrics.destroy();