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.
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();
See also
Metrics And Indexes guides
Rolling Dice demos
Country demo
Todo App demos
Getter methods
This is the collection of getter methods within the Metrics interface. There are 5 getter methods in total.
Listener methods
This is the collection of listener methods within the Metrics interface. There are only two listener methods, addMetricListener and delListener.
Configuration methods
This is the collection of configuration methods within the Metrics interface. There are only two configuration methods, delMetricDefinition and setMetricDefinition.
Iterator methods
This is the collection of iterator methods within the Metrics interface. There is only one method, forEachMetric.
Lifecycle methods
This is the collection of lifecycle methods within the Metrics interface. There is only one method, destroy.
Development methods
This is the collection of development methods within the Metrics interface. There is only one method, getListenerStats.