JSFiddle - React, Tailwind, and code Playground

HTML

<label class="control-label" for="var3">
    <select class="form-control select select-primary select-exemploa" data-toggle="select" name="tvar3" id="var3">
        <option>Selecione um valor</option>
        <option value="value1">value1</option>
        <option value="value2">value2</option>
    </select>
</label>
<div id="div1" style="display:none;">div escondida</div>

JavaScript

$('#var3').on('change', function () {
    if (this.value == 'value2') $("#div1").show();
    else $("#div1").hide();
});

if (2 > 1) {
    $("#var3").val('value2').change();
}