I also implemented a spreadsheet last year [0] in pure TypeScript, with the fun twist that formulas also update backwards. While the backwards root finding algorithm was challenging, I also found it incredibly humbling to discover how much complexity there is in the UX of the simple spreadsheet interface. Handling selection states, reactive updates, detecting cycles of dependency and gracefully recovering from them is a massive state machine programming challenge! Very fun project with a lot of depth!

I myself didn't hand roll my own parser but used Ohm-js [1] which I highly recommend if you want to parse a custom language in Javascript or TypeScript.

> One way of doing this is to keep track of all dependencies between the cells and trigger updates when necessary. Maintaining a dependency graph would give us the most efficient updates, but it’s often an overkill for a spreadsheet.

On that subject, figuring out the efficient way to do it is also a large engineering challenge, and is definitely not overkill but absolutely required for a modern spreadsheet implementation. There is a good description of how Excel does it in this famous paper "Build systems a la carte" paper, which interestingly takes on a spreadsheet as a build system [2].

[0] https://victorpoughon.github.io/bidicalc/

[1] https://ohmjs.org/

[2] https://www.microsoft.com/en-us/research/wp-content/uploads/...

  #define MAXIN 128  // max cell input length
  enum { EMPTY, NUM, LABEL, FORMULA };  // cell types
  struct cell {
    int type;
    float val;
    char text[MAXIN];  // raw user input
  };
  #define NCOL 26    // max number of columns (A..Z)
  #define NROW 50    // max number of rows
  struct grid {
    struct cell cells[NCOL][NROW];
  };

It's not overkill at all. In fact, it's absolutely necessary for all but the simplest toy examples.

Though I think the definition of the parser struct should be

  struct parser {
    const char* s;
    const char* p;
    struct grid* g;
  };

  https://github.com/drclcomputers/GoSheet
  https://github.com/xi/spreadsheet/
  https://github.com/andmarti1424/sc-im
  https://github.com/saulpw/visidata
  https://github.com/bgreenwell/xleak
  https://github.com/SamuelSchlesinger/tshts
  https://github.com/CodeOne45/vex-tui

With MS Edit resurrected similarly, I wonder how hard it would be to get a flushed out text based spreadsheet closer in function to MS Excel or Lotus 123 versions for DOS, but cross platform. Maybe even able to load/save a few different formats from CSV/TSV to XLSX (without OLE/COM embeds).