axax/esnext/lookahead.js

A library of async iterator extensions for JavaScript including ```map```, ```reduce```, ```filter```, ```flatMap```, ```pipe``` and [more](https://github.com/jamiemccrindle/axax/blob/master/docs/API.md#functions).

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const insert_1 = require("./insert");
const iteratorToIterable_1 = require("./iteratorToIterable");
/**
 * Lookahead into the async iteratable
 *
 * @param source The source iterable to look into
 * @param howFar How far to look ahead
 */
function lookahead(howFar) {
    return async function inner(source) {
        const iterator = source[Symbol.asyncIterator]();
        const values = [];
        for (let i = 0; i < howFar; i++) {
            const next = await iterator.next();
            if (next.done) {
                break;
            }
            values.push(next.value);
        }
        return {
            iterable: insert_1.insert(...values)(iteratorToIterable_1.iteratorToIterable(iterator)),
            values,
        };
    };
}
exports.lookahead = lookahead;