You could try to leave out the "liveCode.JStoLC" from the html.
Instead send the conversion 'delayed", 1 tick should be enough:
local svgb="SVGBrowser1"
send "processSVG tID" to widget svgb
put "var dd=document.getElementById('canvas1');" & \
"liveCode.JStoLC(dd.toDataURL(),tID)") into js
send "do js in widget svgb" to me in 1 tick