title: Format Highcharts y-axis labels
body: <p>I'm using Highcharts to generate a line chart that shows currency values. By default the y-axis labels use metric prefixes for abbreviation, e.g. 3k is displayed instead of 3000</p>
  
  <p>I would like to prepend a currency symbol to these labels, e.g. display $3k instead of 3k. However as soon as I add the currency symbol, the metric prefixes are no longer used. I've tried the following</p>
  
  <pre><code>    yAxis: {
          labels: {                
              formatter: function () {
                  return '$' + this.value;
              }
          }
      }
  </code></pre>
  
  <p>and also tried </p>
  
  <pre><code>    yAxis: {
          labels: {
              format: '${value}'
          }
      }
  </code></pre>
  
  <p>But in both cases $3000 is displayed instead of $3k. Is it possible to add a currency symbol without losing the metric prefix?</p>
  
  <p>Here's a demo (<a href="http://jsfiddle.net/x6b0onkp/" rel="noreferrer">JSFiddle here</a>) that illustrates the problem</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$(function() {
    $('#container').highcharts({
  
      yAxis: {
        // if you include the lines below, the metric prefixes disappear
        /*
        labels: {
            format: '${value}'
        }
        */
      },
  
      series: [{
        data: [15000, 20000, 30000]
      }]
  
    });
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"&gt;&lt;/script&gt;
  &lt;script src="https://code.highcharts.com/highcharts.js"&gt;&lt;/script&gt;
  
  &lt;div id="container" style="height: 400px; width: 500px"&gt;&lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>