Question

I’d like to define a relationship between two dom elements (in my particular case, draw lines between to nodes) by clicking on the first followed by a click on the second. The following is my approach. I don’t think it’s particularly elegant or clean. Is there a better way to do this?

$(function() {

   var State = {
      initialClick: false, // tracks clicks status for drawing lines
      initialID: undefined // remember data gotten from the first click
   };

   ...

   $map.on('click', '.node', function() {

     var $this = $(this),
         currentID = $this.attr('data-id');

     if (State.initialClick) {
        if (State.initialID === currentID) {
           // process first click
        } else {
           // process second click
        }

        resetClickTracking();
     } else {
        setState(currentID);
     }
  });

  ...


  function setState(id) {
     State.initialClick = true;
     State.initialID = id;
  }

  function resetState() {
     State.initialClick = false;
     State.initialID = undefined;
  }

});

Answer 1

I would probably go for a delegate pattern:

var lastNodeClicked = null;

$map.on('click', '.node', function() {
    if (lastNodeClicked && lastNodeClicked !== this) {
        // draw line
        lastNodeClicked = null; // reset
    } else {
        lastNodeClicked = this;
    }
});

Instead of resetting the last clicked node, you can also unconditionally update it with the clicked node; that way you can draw lines with less clicks 😉