Mobile viewport height after orientation change

Use the resize event

The resize event will include the appropriate width and height after an orientationchange, but you do not want to listen for all resize events. Therefore, we add a one-off resize event listener after an orientation change:

Javascript:

window.addEventListener('orientationchange', function() {
    // After orientationchange, add a one-time resize event
    var afterOrientationChange = function() {
        // YOUR POST-ORIENTATION CODE HERE
        // Remove the resize event listener after it has executed
        window.removeEventListener('resize', afterOrientationChange);
    };
    window.addEventListener('resize', afterOrientationChange);
});

jQuery:

$(window).on('orientationchange', function() {
    // After orientationchange, add a one-time resize event
    $(window).one('resize', function() {
        // YOUR POST-ORIENTATION CODE HERE
    });
});

Do NOT use timeouts

Timeouts are unreliable - some devices will fail to capture their orientation change within your hard-coded timeouts; this can be for unforeseen reasons, or because the device is slow. Fast devices will inversely have an unnecessary delay in the code.

Gajus' and burtelli's solutions are robust but the overhead is high. Here is a slim version that's reasonably fast in 2017, using requestAnimationFrame:

// Wait until innerheight changes, for max 120 frames
function orientationChanged() {
  const timeout = 120;
  return new window.Promise(function(resolve) {
    const go = (i, height0) => {
      window.innerHeight != height0 || i >= timeout ?
        resolve() :
        window.requestAnimationFrame(() => go(i + 1, height0));
    };
    go(0, window.innerHeight);
  });
}

Use it like this:

window.addEventListener('orientationchange', function () {
    orientationChanged().then(function() {
      // Profit
    });
});