Working with SVG polygon elements

javascript, svg

Solution

No way around it I'm afraid. You have to reconstruct the string again. But it's not difficult to wrap the whole thing in an object, something like:

function Polygon () {
    var pointList = [];
    this.node = document.createElementNS('http://www.w3.org/2000/svg','polygon');
    function build (arg) {
        var res = [];
        for (var i=0,l=arg.length;i<l;i++) {
            res.push(arg[i].join(','));
        }
        return res.join(' ');
    }
    this.attribute = function (key,val) {
        if (val === undefined) return node.getAttribute(key);
        node.setAttribute(key,val);
    }
    this.getPoint = function (i) {return pointList[i]}
    this.setPoint = function (i,x,y) {
        pointList[i] = [x,y];
        this.attribute('points',build(pointList));
    }
    this.points = function () {
      for (var i=0,l=arguments.length;i<l;i+=2) {
          pointList.push([arguments[i],arguments[i+1]]);
      }
      this.attribute('points',build(pointList));
    }
    // initialize 'points':
    this.points.apply(this,arguments);
}

var polygon = new Polygon(0,0, 100,100, 200,200);
polygon.setPoint(0, 50,10); // set point and automatically re-build points
polygon.points(50,50, 50,100, 200,100); // set everything
polygon.node; // refer to the actual SVG element

* not the best implementation but you get the idea.

Problem

I'm trying to work with an SVG polygon and javascript. I create a polygon and set its initial point list like this: ``` var polygon = document.createElementNS('http://www.w3.org/2000/svg','polygon'); polygon.setAttribute("points", "0,0 100,100 200,200"); ``` now what do I do if I want to modify the 2nd point (100,100)? Right now I'm basically reconstructing the whole string again. But can we address "polygon.points" as an array somehow, or is it really just a plain simple string? This can work ok for very simple polygons, but if my polygon eventually has hundreds of point pairs, I'd hate to reconstruct the entire "points" attribute as a string every time I want to modify a single element. Thanks

Original source