Magento 2 Get selected simple product id in configurable product

Got solution. I am writing answer of my question. Hope it will help others.

requirejs(['jquery','underscore'], function(jQuery,_){
    jQuery(window).load(function(){
        jQuery( ".product-options-wrapper div" ).click(function() {
            selpro();
        });
    });
    function selpro () {
        var selected_options = {};
        jQuery('div.swatch-attribute').each(function(k,v){
            var attribute_id    = jQuery(v).attr('attribute-id');
            var option_selected = jQuery(v).attr('option-selected');
            //console.log(attribute_id, option_selected);
            if(!attribute_id || !option_selected){ return;}
            selected_options[attribute_id] = option_selected;
        });

        var product_id_index = jQuery('[data-role=swatch-options]').data('mageSwatchRenderer').options.jsonConfig.index;
        var found_ids = [];
        jQuery.each(product_id_index, function(product_id,attributes){
            var productIsSelected = function(attributes, selected_options){
                return _.isEqual(attributes, selected_options);
            }
            if(productIsSelected(attributes, selected_options)){
                found_ids.push(product_id);
            } 
        });
        console.log(found_ids);
    }
});

For Magento 2.4.0 version, change the below code from

var attribute_id    = jQuery(v).attr('attribute-id');
var option_selected = jQuery(v).attr('option-selected');

to

var attribute_id = jQuery(v).attr('data-attribute-id');
var option_selected = jQuery(v).attr('data-option-selected');

I write js code for get simple product id after selection. You can add following js Code in bottom of this file. app/design/frontend/[your_theme_package]/[your_theme]/Magento_ConfigurableProduct/templates/product/view/type/options/configurable.phtml

<script type="text/javascript">
require(["jquery"], function(jQuery) {
  jQuery(".product-options-wrapper select[id^='attribute']").last().on('change', function() {
      setTimeout(function (){
        simpleId=jQuery("input[name=selected_configurable_option]").val();
        alert(simpleId);
      }, 500); 
  }); }); </script>

Then clear cache, it works for me. See this screenshot: