JSFiddle - React, Tailwind, and code Playground

HTML

<div class="foobar">1</div>
<div class="foo bar">2</div>
<div class="bar foo">3</div>
<div class="barfood">4</div>

JavaScript

function classStartsWith(str) {
      return $('div').map( function(i,e) {
        var classes = e.className.split(' ');
        for (var i=0, j=classes.length; i < j; i++) {
          if (classes[i].substr(0, str.length) == str) return e;
        }
      }).get();
    }

$(classStartsWith('bar')).css('color', 'blue');