Code explanation needed?

JavaScript
1

My version code version is:

const colorScale = d3.scaleThreshold()
    .domain(2.6, 75.1)
    .range(["#fff", "#000"]);

But the code that works is:

const colorScale = d3.scaleThreshold()
    .domain(d3.range(2.6, 75.1, (75.1-2.6)/8)) // can someone explain this line?
    .range(["#fff", "#000"]);

I don’t understand what d3.range() is doing inside .domain()