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import isArray from 'lodash/isArray';
import each from 'lodash/each';
import noop from 'lodash/noop';
import once from './internal/once';
/**
* Runs the `tasks` array of functions in parallel, without waiting until the
* previous function has completed. Once any the `tasks` completed or pass an
* error to its callback, the main `callback` is immediately called. It's
* equivalent to `Promise.race()`.
*
* @name race
* @static
* @memberOf async
* @category Control Flow
* @param {Array} tasks - An array containing functions to run. Each function
* is passed a `callback(err, result)` which it must call on completion with an
* error `err` (which can be `null`) and an optional `result` value.
* @param {Function} callback - A callback to run once any of the functions have
* completed. This function gets an error or result from the first function that
* completed. Invoked with (err, result).
* @example
*
* async.race([
* function(callback) {
* setTimeout(function() {
* callback(null, 'one');
* }, 200);
* },
* function(callback) {
* setTimeout(function() {
* callback(null, 'two');
* }, 100);
* }
* ],
* // main callback
* function(err, result) {
* // the result will be equal to 'two' as it finishes earlier
* });
*/
export default function race(tasks, cb) {
cb = once(cb || noop);
if (!isArray(tasks)) return cb(new TypeError('First argument to race must be an array of functions'));
if (!tasks.length) return cb();
each(tasks, function (task) {
task(cb);
});
}
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