You can't invoke key press with JavaScript.
However, you can control zoom level with JavaScript, here is example for IE and Chrome: http://jsfiddle.net/cMCuz/2/
Edit: now supports Firefox as well.
Required JavaScript:
var _zoomLevel = 100;
function ChangeZoomLevel(diff) {
_zoomLevel += diff;
var oDiv = document.getElementById("Contents");
if (typeof oDiv.style.MozTransform == "string")
oDiv.style.MozTransform = "scale(" + (_zoomLevel / 100) + ")";
else if (typeof oDiv.style.zoom == "string")
oDiv.style.zoom = _zoomLevel + "%";
}
Sample buttons:
<button type="button" onclick="ChangeZoomLevel(10);">+</button>
<button type="button" onclick="ChangeZoomLevel(-10);">-</button>
This will change the zoom level of whole DIV element, can be changed easily to change zoom level of whole document if required.
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