Node.js Callback to Promise Manually promisifying a callback
Example
Sometimes it might be necessary to manually promisify a callback function. This could be for a case where the callback does not follow the standard error-first format or if additional logic is needed to promisify:
Example with fs.exists(path, callback):
var fs = require('fs');
var existsAsync = function(path) {
return new Promise(function(resolve, reject) {
fs.exists(path, function(exists) {
// exists is a boolean
if (exists) {
// Resolve successfully
resolve();
} else {
// Reject with error
reject(new Error('path does not exist'));
}
});
});
// Use as a promise now
existsAsync('/path/to/some/file').then(function() {
console.log('file exists!');
}).catch(function(err) {
// file does not exist
console.error(err);
});
