Bug or not bug? Cannot read property 'clientX' of undefined: firstTouch.clientX in library_sdl.js

[Pavel Duvanov]

Hi, all!

I ran into a problem under mobile browsers, which occurs in the code library_sdl.js:

      switch(event.type) {
        case 'touchstart': case 'touchmove': {
          event.preventDefault();


          var touches = [];
         
          // Clear out any touchstart events that we've already processed
          if (event.type === 'touchstart') {
            for (var i = 0; i < event.touches.length; i++) {
              var touch = event.touches[i];
              if (SDL.downFingers[touch.identifier] != true) {
                SDL.downFingers[touch.identifier] = true;
                touches.push(touch);
              }
            }
          } else {
            touches = event.touches;
          }
         
          var firstTouch = touches[0];
          if (event.type == 'touchstart') {
            SDL.DOMButtons[0] = 1;
          }
          var mouseEventType;
          switch(event.type) {
            case 'touchstart': mouseEventType = 'mousedown'; break;
            case 'touchmove': mouseEventType = 'mousemove'; break;
          }
          var mouseEvent = {
            type: mouseEventType,
            button: 0,
            pageX: firstTouch.clientX,
            pageY: firstTouch.clientY
          };

Question: why is there no verification that the touches array is not empty? I mean this case:

 var firstTouch = touches[0];

Is there bug or not?

Thanks!

--

Pavel Duvanov

[Jukka Jylänki]

Agreed this looks like a bug. Does this kind of fix work? https://github.com/kripken/emscripten/pull/5258

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