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es6-promisify
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promisify.js
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"use strict"; /* global module, require */ module.exports = function () { "use strict"; // Get a promise object. This may be native, or it may be polyfilled var ES6Promise = require("./promise.js"); /** * thatLooksLikeAPromiseToMe() * * Duck-types a promise. * * @param {object} o * @return {bool} True if this resembles a promise */ function thatLooksLikeAPromiseToMe(o) { return o && typeof o.then === "function" && typeof o.catch === "function"; } /** * promisify() * * Transforms callback-based function -- func(arg1, arg2 .. argN, callback) -- into * an ES6-compatible Promise. Promisify provides a default callback of the form (error, result) * and rejects when `error` is truthy. You can also supply settings object as the second argument. * * @param {function} original - The function to promisify * @param {object} settings - Settings object * @param {object} settings.thisArg - A `this` context to use. If not set, assume `settings` _is_ `thisArg` * @param {bool} settings.multiArgs - Should multiple arguments be returned as an array? * @return {function} A promisified version of `original` */ return function promisify(original, settings) { return function () { for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) { args[_key] = arguments[_key]; } var returnMultipleArguments = settings && settings.multiArgs; var target = void 0; if (settings && settings.thisArg) { target = settings.thisArg; } else if (settings) { target = settings; } // Return the promisified function return new ES6Promise(function (resolve, reject) { // Append the callback bound to the context args.push(function callback(err) { if (err) { return reject(err); } for (var _len2 = arguments.length, values = Array(_len2 > 1 ? _len2 - 1 : 0), _key2 = 1; _key2 < _len2; _key2++) { values[_key2 - 1] = arguments[_key2]; } if (false === !!returnMultipleArguments) { return resolve(values[0]); } resolve(values); }); // Call the function var response = original.apply(target, args); // If it looks like original already returns a promise, // then just resolve with that promise. Hopefully, the callback function we added will just be ignored. if (thatLooksLikeAPromiseToMe(response)) { resolve(response); } }); }; }; }();