needed a simple circle legend for a bubble chart that I could pass in values and a domain

to initiate pass in a d3 selection to the circleLegend function and your dataset domain and values:

    var l = circleLegend(d3.select('svg g#legend'))
        .domain([0, 100])) // the dataset min and max
        .range( [0, 80]) // the circle area/size mapping
        .values( [8, 34, 89]) // pass in values (e.g. min,mean/median & max)
        // optional
        .width(500) // it centers to this
        .height( 500) // it centers to this
        .suffix('') // ability to pass in a suffix e.g. '%'
        .circleColor( '#888') // stroke of the circles
        .textPadding(40) // left padding on text
        .textColor( '#454545') // the fill for text

    // and render it
    l.render()

note: the number of values you pass in will correlate to the number of circles

forked from <a href='http://bl.ocks.org/eesur/'>eesur</a>'s block: <a href='http://bl.ocks.org/eesur/7b63401950344f2dca1025d09cc7386d'>d3 | reusable circle legend</a>