InspectSequenceclass

new InspectSequence<T, R, N>()

Return
`InspectSequence<T, R, N>`	Sequence of values that inspects a source sequence of values as it iterates.

Property	Type
`.count`	`unknown`	The number of values yielded by the source sequence so far. required readonly
`.done`	`unknown`	Whether the source sequence has finished iterating (i.e. it has returned). required readonly
`.first`	`T`	The first value yielded by the source sequence. - Throws if the iteration yielded no values yet, i.e. `this.count === 0`. required readonly
`.last`	`T`	The last value yielded by the source sequence. - Throws if the iteration yielded no values yet, i.e. `this.count === 0`. required readonly
`.returned`	`R`	The value returned by the source sequence when it finished. - Throws if the iteration is not done yet, i.e. `this.done === false`. readonly

Sequence of values that inspects a source sequence of values as it iterates.

Stores: first/last yielded value, returned value, whether iteration is done, the number of items that were iterated.

A ThroughSequence that records what passes through it without changing the values. As it iterates a source sequence it tracks the first and last yielded values, the count of values, whether iteration is done, and the final returned value.

Useful in tests and diagnostics when you need to assert on what a sequence produced.

Usage

import { InspectSequence } from "shelving/sequence";

async function* numbers() {
  yield 10; yield 20; yield 30;
}

const watch = new InspectSequence(numbers());
for await (const n of watch) {
  console.log("yielded", n);
}

console.log(watch.count);  // 3
console.log(watch.first);  // 10
console.log(watch.last);   // 30
console.log(watch.done);   // true

first, last, and returned throw an UnexpectedError if read before the relevant values exist — e.g. first before iteration has yielded anything, or returned before iteration is done.

Examples

const watch = new InspectSequence(iterable);
	for await (const next of capture) console.log("YIELDED", next);
	console.log("FIRST", watch.first);
	console.log("RETURNED", watch.returned);