Get pixel length of String in Svg

Question

I'm currently working with SVG. I need to know the string length in pixels in order to do some alignment. How can I do to get the length of a string in pixel ?

Update: Thanks to nrabinowitz. Based on his help, I can now get the length of dynamic-added text. Here is an example:

<svg id="main" 
    xmlns="http://www.w3.org/2000/svg" 
    xmlns:xlink="http://www.w3.org/1999/xlink"
    version="1.1" 
    width="1020"
    height="620" 
    viewBox="0 0 1020 620"
    onload="startup(evt)">

<script>
    <![CDATA[
        var startup = function (evt) {
            var width;
            var svgNS = "http://www.w3.org/2000/svg";
            var txtNode = document.createTextNode("Hello");
            text = document.createElementNS(svgNS,"text");

            text.setAttributeNS(null,"x",100);
            text.setAttributeNS(null,"y",100);
            text.setAttributeNS(null,"fill","black");
            text.appendChild(txtNode);                                              
            width = text.getComputedTextLength();               
            alert(" Width before appendChild: "+  width);                       
            document.getElementById("main").appendChild(text);
            width = text.getComputedTextLength();
            alert(" Width after appendChild: "+  width)
            document.getElementById("main").removeChild(text);              
        }       
    //]]>
</script>
</svg>

Answer 1

I've been wondering this too, and I was pleasantly surprised to find that, according to the SVG spec, there is a specific function to return this info: getComputedTextLength()

// access the text element you want to measure
var el = document.getElementsByTagName('text')[3];
el.getComputedTextLength(); // returns a pixel integer

Working fiddle (only tested in Chrome): http://jsfiddle.net/jyams/

Answer 2

Having read various similar threads with interest and benefitted from some of the ideas, I've created a page which compares three of the Javascript methods side-by-side. I've noted results in

IE9

Firefox 29.0.1 and

Chrome 34.0.1847.131 m

You can load it in your browser and see what works for you:

http://bl.ocks.org/MSCAU/58bba77cdcae42fc2f44 .