Add alert after page load - TYPO3

Question

I have the standard bootstrap package and want to show an alert after the page is beeing laoded. May the alert will only shown at the index-site.

Anybody know how to do this?

I tried to include own javascript, but that doesnt worked for me..

TS:

page.includeJS.file1 = fileadmin/myTemplates/alert.js

alert.js:

window.onload = function () {
    alert('My Alert!');
};

Answer 1

Found an solution. I looked for the path of an already includes js file and paste my code in. I think it isnt the perfect solution, but it works first.

file i added my script: /typo3conf/ext/bootstrap_package/Resources/Public/JavaScript/Libs/modernizr...