doWhilst.js

import noop from 'lodash/noop';
import rest from './internal/rest';

import onlyOnce from './internal/onlyOnce';

/**
 * The post-check version of [`whilst`]{@link module:ControlFlow.whilst}. To reflect the difference in
 * the order of operations, the arguments `test` and `iteratee` are switched.
 *
 * `doWhilst` is to `whilst` as `do while` is to `while` in plain JavaScript.
 *
 * @name doWhilst
 * @static
 * @memberOf module:ControlFlow
 * @method
 * @see [async.whilst]{@link module:ControlFlow.whilst}
 * @category Control Flow
 * @param {Function} iteratee - A function which is called each time `test`
 * passes. The function is passed a `callback(err)`, which must be called once
 * it has completed with an optional `err` argument. Invoked with (callback).
 * @param {Function} test - synchronous truth test to perform after each
 * execution of `iteratee`. Invoked with the non-error callback results of 
 * `iteratee`.
 * @param {Function} [callback] - A callback which is called after the test
 * function has failed and repeated execution of `iteratee` has stopped.
 * `callback` will be passed an error and any arguments passed to the final
 * `iteratee`'s callback. Invoked with (err, [results]);
 */
export default function doWhilst(iteratee, test, callback) {
    callback = onlyOnce(callback || noop);
    var next = rest(function(err, args) {
        if (err) return callback(err);
        if (test.apply(this, args)) return iteratee(next);
        callback.apply(null, [null].concat(args));
    });
    iteratee(next);
}