That's really a question of the APIs you're using rather than the language. If you're using a browser, you don't even need JS to draw the line; you can just go to this URL:

    data:text/html,<svg><line x1=0 y1=30 x2=40 y2=50 stroke=black>

If you're using an API other than the browser, it can be super simple. Like, with processing.js, http://sketchpad.cc/sp/pad/view/zdsBK2b9xo/latest consists of:

    line(0, 30, 40, 50);

and that works. (Although you could surely argue that the language of processing.js isn't itself JS, but you can invoke its facilities from JS.)

There are also clumsier ways to draw lines, like with DOM manipulation in SVG or drawing stuff on a <canvas>, and those might be desirable for the extra flexibility they give you. But you don't have to start with them.