NodeJS: the beautiful callback err machine

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One of the best things about NodeJS callbacks is their consistency. As in, most API calls require one and their method signature always follows the same pattern, and this is the most beautiful bit.

The first parameter of a callback is always an error object (which is null if no error occurred). This seems a little counterintuative at first. When you stop and think about it though, it really isn’t at all. My initial though was that most of the time, it isn’t going to be used, so why isn’t the result of the computation the first parameter? Well, that might be nice, but chances are you’re actually going to have to check to see if an error occurred first, before you start using your results, since if a error did occur, you probably don’t have any results anyway! Secondly, Node is cleverly reminding you that you should check for and deal with errors as they happen by ensuring you define a first parameter in order to define a second parameter to get at the stuff you want.

If the error was the second (or last) parameter the chances are you’d forget to define it, or the lazy would simply neglect to define it. This could happen because in JavaScript all parameters to functions are optional. Just because you do or don’t define parameters to a function, doesn’t mean you can’t call it with or without parameters. The function might not work in either of these cases, but nevertheless it is still possible to call it. It seems that by not coercing the programmer into defining an error parameter and dealing with it their code could become less robust.

The error parameter in the callback function is a necessity of asynchronous programming because errors cannot usually caught with a try/catch block as the execution of the callback function usually doesn’t happen in the block of code surrounded by the try/catch but instead in a later run of the event loop. I much prefer this way of dealing with errors as opposed to searching through my library code to find out if I even need to surround a function call in a try/catch by figuring out if it even does an operation that could possibly throw an error…and you know what, it’s future proof, because even if a function does no operations that could cause an error, it doesn’t mean that in a future version it won’t. By defining an error parameter from the start you can deal with a future mishap, now that is awesome.

22,131 thoughts on “NodeJS: the beautiful callback err machine”

  25. Lady Gaga lived up to her fashion icon status for the London premiere of The Joker:
    Folie à Deux on Wednesday night with three outfit changes. 

    The singer, 38, who plays Harley Quinn in film, commanded attention as she left the afterparty at Nomad Hotel in Covent Garden in an outlandish face print bodysuit
    and matching stockings. 

    The pattern had drawings of bleeding faces stitched together and matched Gaga’s perfectly themed eye-shadow look for the psychopathic character
    in which she portrays. 

    Gaga had originally arrived to afterparty in a striped
    minidress after wowing on the red carpet in a custom scarlet Celine
    gown – and she made sure her outfit was still a talking point when she left the bash with her fiancé Michael Polansky,
    46. 

    Despite leaving in the early hours, Gaga donned a pair of dark shades and added to
    her quirky look with ripped tights and baby blue platform
    heels. 

    Lady Gaga lived up to her fashion icon status for the London premiere
    of The Joker: Folie à Deux on Wednesday night with three outfit changes

    The singer, 38, who plays Harley Quinn in film, commanded attention as she left the afterparty at Nomad Hotel in Covent Garden in an outlandish face print
    bodysuit and matching stockings

    The pattern had drawings of bleeding faces stitched together and matched Gaga’s perfectly themed eye-shadow
    look for the psychopathic character she portrays

    Earlier on in the evening, Gaga looked great in a blue and beige striped dress and
    quirky tights as she headed to a fan event with her fiancé
    Michael.

    The star wore her dyed red tresses in a short cropped style and opted for a red lip and face makeup. 

    She boosted her height with huge black shiny heels as she walked besides her partner who wore all black.

    The singer turned actress takes a starring role as Harley in the psychological
    thriller, in which Joaquin Phoenix reprises his role as the titular Joker – Batman’s soon-to-be nemesis. 

    Arriving at Cineworld Leicester Square alongside ever-supportive fiancé Michael, Gaga looked incredible in a custom-made gown from Celine by Hedi Slimane as she greeted fans at the premiere. 

    The structured number featured dramatic shoulder pads and a plunging
    neckline which showed off her figure as she posed up a storm. 

    Gaga’s fashion parade for the film has been a resounding success at least after her last big film House of Gucci released in 2021 was savaged by
    critics.

    She wore her dyed-red tresses in a short cropped style and
    wore blue eye makeup complete with perfect sequin detailing on one side of her face.

    The songstress made sure her outfit was still a talking point when she left the bash with her fiancé Michael
    Polansky, 46

    Earlier on in the evening, Gaga looked great in a blue and beige striped dress and
    quirky tights as she headed to a fan event with her fiancé Michael

    Gaga drew a crowd of fans as she arrived at the Nomad
    Hotel 

    The actress looked in her element in the quirky outfit 

    For the premiere, the singer looked incredible in a custom-made gown from Celine by
    Hedi Slimane as she greeted fans at the event in central
    London

    The singer turned actress takes a starring role as Harley Quinn in the psychological thriller, in which Joaquin reprises
    his role as the titular Joker – Batman’s soon-to-be nemesis

    She couldn’t resist packing on the PDA with Michael on the night

    Gaga pictured as Harley Quinn in the new film. It is the much-anticipated follow-up to 2019′s Academy
    Award-winning Joker, which earned more than $1 billion at the global box office

    Gaga was swarmed by fans as she made her way to the afterparty  

    The star wore her dyed red tresses in a short cropped style and opted for a red
    lip and face makeup

    She boosted her height with huge black shiny heels as she walked besides her partner who wore all black

    Folie à Deux will see Joaquin, 49, reprise his role as Arthur Fleck AKA Joker and he
    arrived to the premiere in a black jacket and tie 

    Meanwhile, businessman Michael looked effortlessly
    dapper in a black suit, crisp white shirt and
    tie as he put his arm around his future wife.

    She gazed adoringly at Michael as she flashed her enormous 8 carat engagement ring on the star-studded red carpet.

    Folie à Deux will see Joaquin, 49, reprise his role as Arthur Fleck AKA Joker.

    It is the much-anticipated follow-up to 2019′s
    Academy Award-winning Joker, which earned more
    than $1 billion at the global box office and remains the highest-grossing R-rated film
    of all time.

    Set for release on October 4, the second instalment finds Arthur Fleck institutionalised
    at Arkham awaiting trial for his crimes as Joker.

    ‘While struggling with his dual identity, Arthur not only stumbles upon true love, but also finds
    the music that’s always been inside him,’ a press release shared.

    Lady Gaga has been supported by her fiancé Michael in the lead up to the thriller’s premiere. 

    The couple was first romantically linked around New Year’s Eve 2019 and later went Instagram official in early 2020.

    Lady GagaJoaquin Phoenix

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  50. A Danish student who was dubbed a ‘real-life Cinderella’
    after leaving one of her golden stilettos at the future
    king’s birthday bash has found her very own ‘Prince Charming’. 

    Anne-Sofie Tornso Olesen left one of her high heels at the end of
    Prince Christian of Denmark’s 18th birthday party in October last year.

    Unlike in the fairy tale, Anne-Sofie’s missing shoe was returned not by the Prince but by a postman, after a picture
    of the heel was posted by the royal family on social media.

    However, Anne-Sofie has since found love in 20-year-old Nikolas Kolding, who works at Tivoli Gardens amusement park in the Danish capital Copenhagen.

    ‘We met in Tivoli,’ she said. ‘I was out with my friend.
    I thought he looked cute, so I went up to him and asked for his socials.

    ‘He took me on the most adorable date a few days later’ – a picnic
    in the forest. 

    The 19-year-old actress added: ‘To me, he is like royalty.’

    Anne-Sofie meeting the then Danish Queen Margrethe II at Prince Christian’s 18th birthday party.
    She left her golden stiletto at the palace – although it was not returned to her by the Prince

    The Danish student has now found her own Prince Charming in Nikolas Kolding who works at Tivoli Gardens amusement park in Copenhagen

    Anne-Sofie’s golden high heel was returned to her
    after the royal family published an Instagram photo of the shoe found at Christiansborg Palace in October last year

    Actress Anne-Sofie (pictured left), joked leaving the shoe at the party
    ‘was meant to be a fairytale ending à la Cinderella.’
    Pictured right: Prince Christian

    Anne-Sofie was invited to Prince Christian’s party
    to represent the area where she lives outside the Danish capital,
    having won the invitation in a tombola.

    She sported a sheer black dress at the reception and even greeted Denmark’s then Queen Margrethe II, her son, Crown Prince Frederik and
    his son Prince Christian, who were all oblivious to her ‘funny’ attempt to steal the show.

    The actress said at the time: ‘I thought it was a bit funny myself,
    and I talked to my family and friends about it before, and they agreed that I should do it.
    It’s a chance you won’t get again.

    ‘It’s not because I think that now I’m going to marry him, but I kind of hoped that someone would think
    it was funny, and then it also creates attention for the royal house.’ 

    The student did speak to the Prince at his celebration, although she
    couldn’t remember the exact conversation.

    ‘I don’t really remember what I asked about,
    because I was so confused, but I think it had something to
    do with what he thought about the whole thing – and about having invited all those people into the castle,’ she said.

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