Onmousemove And Onmousedown

I am new to JavaScript and kind of confused as to why my onmousedown together with onmousemove condition is not being implemented. Here is what I have:
1) SVG code calling JavaScript function

<g id="0" style="display:inline;fill-rule:evenodd">
<desc>0</desc>
<image id="image_url0" xlink:href="draw_svg.svg" width="1000" height="1000" onmousedown="doZoom(evt, 1);" onmousemove="doZoom(evt, 1);" onmouseup="doZoom(evt, 1);" />
</g>

2) JavaScript function:

function doZoom(evt, current) {
//THIS SHOULD WORK
if (evt.type == "mousedown" && evt.type == "mousemove" ) {
var SVGDoc = evt.getTarget().getOwnerDocument();
var SVGChild = SVGDoc.getElementById("maps");
var svgobj = SVGChild.getElementById("0");
svgobj.getStyle().setProperty('display', 'none');
} }

But the code works only if I say: 'if (evt.type == "mousedown") without "mousemove" . Please note, that I am calling my function onmousemove event also so it should register. I will very much appreciate if somebody could tell me why 'mousemove' AND 'mousedown' both don't work in my 'If' statement.