JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div>
        <div class="block-1">1</div>
    </div>
    <div>
        <div>
            <div class="block-45">2</div>
        </div>
    </div>
    <div>
        <div>
            <div>
                <div class="block-312">3</div>
            </div>
        </div>
    </div>
</div>

JavaScript

function func(a,b){
	var setEl  = $(a),
      nextEl =false, 
      text;
      setEl.each(function(i){
         if($(this).is(b)){
            if(setEl.eq(i+1).length > 0){
              nextEl = setEl.eq(i+1);
            } 
          return false;
       }
    })
      
    text = nextEl?nextEl.text():"";
    console.log(text) 
};

func("[class*='block-']",".block-1")