<div class="pp-buttons-container">
    <button class="import" id="<?php echo $block->getId() ?>" onclick="return false;">
        <span><span><span><?php echo 'Import'; ?></span></span></span>
    </button>
</div>
<script type="text/javascript">
    require(["jquery",'mage/url'], function($, url){
        "use strict";
        $(document).on('click','.col-action-grouped a',function(){
        });

        $(document).on('click','.import',function(){
            jQuery.ajax({
            url: '/admin/customimport/index/import',
            type: "POST",
            data: {data:'success'},
            success: function(response){
                console.log('ABCD');
            }
        });
        });

    });
</script>

<?php

namespace ECCustomimportControllerAdminhtmlIndex;

use ECCustomimportModelCustomimportFactory;
use MagentoFrameworkControllerResultFactory;
use MagentoBackendAppActionContext;

class Import extends MagentoBackendAppAction
{
    protected $request;

    /**
     * @param Context $context
     */
    public function __construct(
        MagentoFrameworkAppRequestHttp $request,
        Context $context,
        CustomimportFactory $modelCustomimportFactory
    ) {
        $this->request = $request;
        $this->modelCustomimportFactory = $modelCustomimportFactory;
        $this->resultFactory = $context->getResultFactory();
        parent::__construct($context);
    }

    public function execute(){
        ignore_user_abort(true);
        set_time_limit(0);

        $id = $this->request->getParams(); // all params
        print_r($id);
        exit;

        $model  = $this->modelCustomimportFactory->create()->load($id);
        $model->import();
        $resultRedirect = $this->resultFactory->create(ResultFactory::TYPE_REDIRECT);
        $resultRedirect->setPath('adminhtml/*/index');
        return $resultRedirect;
    }
}

$id = $this->request->getParams('data'); // all params
print_r($id);