D3 4.x: axis & time scale issue

time.js

var now = new Date();
var then = new Date();
then.setDate(now.getDate() + 7);

var axis = d3.axisTop().ticks(d3.timeDays).tickFormat(d3.timeFormat('%b %d'));
var scale = d3.scaleTime().domain([now, then]).range([0, 500]);

axis.scale(scale);

d3.select(document.body).append('svg').append('g').call(axis); // TypeError: t.range is not a function