how to add script before </body> in magento 2

Add referenceContainer code in layout file

app/design/frontend/<vendor>/<theme>/Magento_Theme/layout/default.xml

Before body end

 <referenceContainer name="before.body.end">
      <block class="Magento\Framework\View\Element\Js\Components" name="js.beforebody" as="jsbeforebody" template="Magento_Theme::js/js.phtml"/>
    </referenceContainer>
For after body start

 <referenceContainer name="after.body.start">
      <block class="Magento\Framework\View\Element\Js\Components" name="js.afterbody" as="jsafterbody" template="Magento_Theme::js/js.phtml"/>
    </referenceContainer>
Create js.phtml template file and put your js script/code in this file.

app/design/frontend/<vendor>/<theme>/Magento_Theme/templates/js/js.phtml