Utility function to convert a function with signature fn(args, cb(err, result)) to return a promise

promisify.js

//Utility function to convert a function with signature fn(args, cb(err, result)) to return a promise
function promisify ( fn, context ) {
    return function () {
        var args = [].slice.call( arguments );
        return new Promise( function ( fulfil, reject ) {
            var callback = function ( err ) {
                if ( err ) return reject( err );
                fulfil.apply( null, [].slice.call( arguments, 1 ) );
            };
            args.push( callback );
            fn.apply( context, args );
        });
    };
};

Example...

var hello = function(msg, cb){cb(null, "Hello from " + msg)}
var result = await promisify(myFn)(arg1, arg2, arg3)