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67 lines
2.3 KiB
JavaScript
67 lines
2.3 KiB
JavaScript
6 years ago
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'use strict';
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Object.defineProperty(exports, "__esModule", {
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value: true
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});
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exports.default = ensureAsync;
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var _setImmediate = require('./internal/setImmediate');
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var _setImmediate2 = _interopRequireDefault(_setImmediate);
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var _wrapAsync = require('./internal/wrapAsync');
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function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
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/**
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* Wrap an async function and ensure it calls its callback on a later tick of
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* the event loop. If the function already calls its callback on a next tick,
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* no extra deferral is added. This is useful for preventing stack overflows
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* (`RangeError: Maximum call stack size exceeded`) and generally keeping
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* [Zalgo](http://blog.izs.me/post/59142742143/designing-apis-for-asynchrony)
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* contained. ES2017 `async` functions are returned as-is -- they are immune
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* to Zalgo's corrupting influences, as they always resolve on a later tick.
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*
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* @name ensureAsync
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* @static
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* @memberOf module:Utils
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* @method
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* @category Util
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* @param {AsyncFunction} fn - an async function, one that expects a node-style
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* callback as its last argument.
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* @returns {AsyncFunction} Returns a wrapped function with the exact same call
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* signature as the function passed in.
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* @example
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*
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* function sometimesAsync(arg, callback) {
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* if (cache[arg]) {
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* return callback(null, cache[arg]); // this would be synchronous!!
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* } else {
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* doSomeIO(arg, callback); // this IO would be asynchronous
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* }
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* }
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*
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* // this has a risk of stack overflows if many results are cached in a row
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* async.mapSeries(args, sometimesAsync, done);
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*
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* // this will defer sometimesAsync's callback if necessary,
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* // preventing stack overflows
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* async.mapSeries(args, async.ensureAsync(sometimesAsync), done);
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*/
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function ensureAsync(fn) {
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if ((0, _wrapAsync.isAsync)(fn)) return fn;
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return function (...args /*, callback*/) {
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var callback = args.pop();
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var sync = true;
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args.push((...innerArgs) => {
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if (sync) {
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(0, _setImmediate2.default)(() => callback(...innerArgs));
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} else {
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callback(...innerArgs);
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}
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});
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fn.apply(this, args);
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sync = false;
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};
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}
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module.exports = exports['default'];
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