SVG standard allows to use and refer external SVG files.
I have a file circle.svg that defines a circle object with id \"the_circle\". From the main SVG
circle.svg
To supplement @echo-flow's excellent solution with the code in jQuery/Coffeescript:
$.get '/assets/hexagon.svg', (svgFileData)-> svgTag = svgFileData.documentElement $('body').append(svgTag) circle = $('#the_circle')