爱好者自学,请大神帮忙解释,javascript中应用API

各位大神，目前小弟正在自学，有一问题请教，先谢谢了
就是通过API在网页上显示比特时代的API
http://api.btc38.com/v1/ticker.php?c=ltc&mk_type=cny
返回是
{"ticker":{"high":437,"low":408,"last":415.95,"vol":38335.11643,"buy":413,"sell":415.99}}
我在网上查的方法是：
http://m.blog.csdn.net/live4what/article/details/26230177这篇文章里的方法二<script type="text/javascript">
  var url = "https://data.btcchina.com/data/ticker?et=btccny";
  $.getJSON(url, function(data){      
        document.write(data+"<br>" );
        document.write(data.ticker+"<br>" );
        document.write("btc="+data.ticker.high+"<br>" );
        document.write(data.ticker.sell+"<br>" );
        
  } );    
</script>这个JS返回的是{"ticker":{"high":"0.00","low":"0.00","buy":"0.00","sell":"0.00","last":"28158.00","vol":"0.00000000","date":1508143042,"vwap":0,"prev_close":28158,"open":0}}我用这个方法去试比特时代的链接，是不行的，后来发现是因为价格没有双引号，请问大神怎么提取数据呀最好给个实例，再次谢谢