highlightjs add language class to all code blocks

highlight.html

<!-- if you are using sublime, uncomment to get a snippet
<snippet>
    <content><![CDATA[
-->
<link rel="stylesheet" href="PATH_TO_YOUR_CSS\highlight\styles\github.css">
<script src=PATH_TO_YOUR_JS\highlight\highlight.pack.js"></script>
<script>hljs.initHighlightingOnLoad();
let addLangClass = function () {
  document.getElementByTagName("code").classList.add("${1:language}");
}
if(window.attachEvent) {
    window.attachEvent('onload', addLangClass);
} else {
    if(window.onload) {
        let curronload = window.onload;
        let newonload = function(evt) {
            curronload(evt);
            addLangClass();
        };
        window.onload = newonload;
    } else {
        window.onload = addLangClass;
    }
}
</script>
<!-- if you are using sublime, uncomment the following to get a snippet
    ]]></content>
    <!-- Optional: Set a tabTrigger to define how to trigger the snippet -->
    <tabTrigger>highlight</tabTrigger>
    <!-- Optional: Set a scope to limit where the snippet will trigger -->
    <!-- <scope>source.python</scope> -->
</snippet>
-->