How do I stop a runaway setInterval() timer in JavaScript

Question

setInterval hangs when I hold the left mouse button down and sequentially press the right button. setInterval will not clear after that.

    var timer = 0;

    document.getElementById('c_3').onmousedown = function(e) {

          timer = setInterval(function() {myFunction();}, 30);

          if (e.which == 2 || e.which == 3) {

                clearInterval(timer);

          }

    }

Answer 1

This is how it works now ...

    let timer = 0;

    document.getElementById('c_3').onmousedown = function(e) {

      if (e.which == 1) {

        timer = setInterval(function() {myFunction();}, 30);

      }

      if (e.which == 2 || e.which == 3) {

        document.getElementById('c_3').oncontextmenu = function() {

          return false;

        }

        clearInterval(timer);

      }

    }

    document.getElementById('c_3').onmouseup = function() {

        clearInterval(timer);

    }