shelving/util/iterate.js

Toolkit for using data in JavaScript.

/** Is an unknown value an iterable? */
export const isIterable = (value) => typeof value === "object" && !!value && Symbol.iterator in value;
/** Flatten one or more iterables. */
export function* flattenItems(items) {
    if (isIterable(items))
        for (const item of items)
            yield* flattenItems(item);
    else
        yield items;
}
/**
 * Does an iterable have one or more items.
 * - Checks `items.size` or `items.length` first, or consumes the iterable and counts its iterations.
 */
export function hasItems(items) {
    for (const unused of items)
        return true;
    return false;
}
/** Count the number of items in an iterable. */
export function countItems(items) {
    let count = 0;
    for (const unused of items)
        count++;
    return count;
}
/**
 * Yield a range of numbers from `start` to `end`
 * - Yields in descending order if `end` is lower than `start`
 */
export function* getRange(start, end) {
    if (start <= end)
        for (let num = start; num <= end; num++)
            yield num;
    else
        for (let num = start; num >= end; num--)
            yield num;
}
/**
 * Apply a limit to an iterable set of items.
 * - Checks `items.size` or `items.length` first to see if the limit is necessary.
 */
export function* limitItems(items, limit) {
    let count = 0;
    if (count >= limit)
        return;
    for (const item of items) {
        yield item;
        count++;
        if (count >= limit)
            return;
    }
}
/** Pick items from an iterable set of items. */
export function* pickItems(items, ...pick) {
    for (const item of items)
        if (pick.includes(item))
            yield item;
}
/** Omit items from an iterable set of items. */
export function* omitItems(items, ...omit) {
    for (const item of items)
        if (!omit.includes(item))
            yield item;
}
export function reduceItems(items, reducer, initial) {
    let current = initial;
    for (const item of items)
        current = reducer(current, item);
    return current;
}
/** Yield chunks of a given size. */
export function* getChunks(items, size) {
    let chunk = [];
    for (const item of items) {
        chunk.push(item);
        if (chunk.length >= size) {
            yield chunk;
            chunk = [];
        }
    }
    if (chunk.length)
        yield chunk;
}
/** Merge two or more iterables into a single iterable set. */
export function* mergeItems(...inputs) {
    for (const input of inputs)
        yield* input;
}