[javascript] Disable scrolling in an iPhone web application?

document.addEventListener('touchstart', function (e) {
    e.preventDefault();
});

Do not use the ontouchmove property to register the event handler as you are running at risk of overwriting an existing event handler(s). Use addEventListener instead (see the note about IE on the MDN page).

Beware that preventing default for the touchstart event on the window or document will disable scrolling of the descending areas.

To prevent the scrolling of the document but leave all the other events intact prevent default for the first touchmove event following touchstart:

var firstMove;

window.addEventListener('touchstart', function (e) {
    firstMove = true;
});

window.addEventListener('touchmove', function (e) {
    if (firstMove) {
        e.preventDefault();

        firstMove = false;
    }
});

The reason this works is that mobile Safari is using the first move to determine if body of the document is being scrolled. I have realised this while devising a more sophisticated solution.

In case this would ever stop working, the more sophisticated solution is to inspect the touchTarget element and its parents and make a map of directions that can be scrolled to. Then use the first touchmove event to detect the scroll direction and see if it is going to scroll the document or the target element (or either of the target element parents):

var touchTarget,
    touchScreenX,
    touchScreenY,
    conditionParentUntilTrue,
    disableScroll,
    scrollMap;

conditionParentUntilTrue = function (element, condition) {
    var outcome;

    if (element === document.body) {
        return false;
    }

    outcome = condition(element);

    if (outcome) {
        return true;
    } else {
        return conditionParentUntilTrue(element.parentNode, condition);
    }
};

window.addEventListener('touchstart', function (e) {
    touchTarget = e.targetTouches[0].target;
    // a boolean map indicating if the element (or either of element parents, excluding the document.body) can be scrolled to the X direction.
    scrollMap = {}

    scrollMap.left = conditionParentUntilTrue(touchTarget, function (element) {
        return element.scrollLeft > 0;
    });

    scrollMap.top = conditionParentUntilTrue(touchTarget, function (element) {
        return element.scrollTop > 0;
    });

    scrollMap.right = conditionParentUntilTrue(touchTarget, function (element) {
        return element.scrollWidth > element.clientWidth &&
               element.scrollWidth - element.clientWidth > element.scrollLeft;
    });

    scrollMap.bottom =conditionParentUntilTrue(touchTarget, function (element) {
        return element.scrollHeight > element.clientHeight &&
               element.scrollHeight - element.clientHeight > element.scrollTop;
    });

    touchScreenX = e.targetTouches[0].screenX;
    touchScreenY = e.targetTouches[0].screenY;
    disableScroll = false;
});

window.addEventListener('touchmove', function (e) {
    var moveScreenX,
        moveScreenY;

    if (disableScroll) {
        e.preventDefault();

        return;
    }

    moveScreenX = e.targetTouches[0].screenX;
    moveScreenY = e.targetTouches[0].screenY;

    if (
        moveScreenX > touchScreenX && scrollMap.left ||
        moveScreenY < touchScreenY && scrollMap.bottom ||
        moveScreenX < touchScreenX && scrollMap.right ||
        moveScreenY > touchScreenY && scrollMap.top
    ) {
        // You are scrolling either the element or its parent.
        // This will not affect document.body scroll.
    } else {
        // This will affect document.body scroll.

        e.preventDefault();

        disableScroll = true;
    }
});

The reason this works is that mobile Safari is using the first touch move to determine if the document body is being scrolled or the element (or either of the target element parents) and sticks to this decision.