multitude/dist/push/operators/consume/first.js

Comprehensive streams for push and pull

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.first = first;

var _transform = require("../../utils/transform");

var _take = require("../filter/take");

var _pipettes = require("pipettes");

/**
 * Returns a *Promise* of the first value an *Observable* emits.
 * Such *Promise* will reject if the *Observable* errors
 * before emitting a value.
 * @param strict if `true`, the returned *Promise* will reject if the *Observable* completes before emitting a value instead of resolving with undefined.
 */
function first(strict) {
  return (0, _transform.transform)(observable => {
    let emitted = false;
    return new Promise((resolve, reject) => {
      (0, _pipettes.into)(observable, (0, _take.take)(1)).subscribe({
        next(value) {
          emitted = true;
          resolve(value);
        },

        error(reason) {
          emitted = true;
          reject(reason);
        },

        complete() {
          if (emitted) return;

          if (strict) {
            reject(Error(`Observable completed before emitting a value`));
          } else {
            resolve();
          }
        }

      });
    });
  });
}
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