Created
December 12, 2018 13:20
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Simple async functionality for native style nodeJS functions
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| // The normal async programming flow in nodeJS can get hairy, quickly: | |
| function readAndParse(filename, callback){ | |
| fs.readFile(filename, 'utf8', (err, data) => { | |
| if(err){ | |
| callback(err, null); | |
| return; | |
| } | |
| myParser.doParsing(data, (err, result) => { | |
| if(err){ | |
| callback(err, null); | |
| return; | |
| } | |
| callback(null, result); | |
| }); | |
| }); | |
| } | |
| // With a small helper function, this nested callback construction can be flattened to this: | |
| async function readAndParse(filename){ | |
| const src = await asPromise(fs.readFile, filename, 'utf8'); | |
| const result = await asPromise(myParser.doParsing, src); | |
| return result; | |
| } | |
| // This is the wrapper function `asPromise`, that can take any nodeJS callback style function and wrap it into a promise: | |
| /** | |
| * Converts a nodeJS native style function and calls it as a promise. | |
| * @param {function} normalFunc The original nodeJS function to wrap in a promise. | |
| * @param {any...} normalArguments Any arguments you want to pass to the wrapped function. | |
| * @returns {Promise<any>} | |
| */ | |
| const asPromise = (normalFunc, ...normalArguments) => new Promise((resolve, reject) => { | |
| const combinedArguments = [...normalArguments, function () { | |
| const [err, ...rest] = arguments; | |
| if (err) { | |
| reject(err); | |
| } | |
| resolve.apply(normalFunc, rest); | |
| }]; | |
| normalFunc.apply(normalFunc, combinedArguments); | |
| }); |
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