path dimensions

Does anyone know if you can change the dimensions of a path by using a function to set them. See i want to click on a button and make a line appear, so i set the dimensions to zero so its not there, but i want the dimensions below to appear when i click on “smokeNext”. Bottom part is SVG

function smoke(evt){

cig.setAttribut(“d”, M 837 452 L 726 400);
}

</script>

<path id=”smokeNext” onclick=”smoke()”
d=”M 260 770 L 280 785 260 800 z”
style=”stroke:black; stroke-width:3; fill:blue”>
<set attributeName=”fill” to=”red”
begin=”smokeNext.mouseover”
end=”smokeNext.mouseout”/>
</path>

<path id=”cig” d=”M 0 0 L 0 0″
style=”fill:none;stroke:white;stroke-width:16″/>

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