Answer 1

var langs = ['html', 'css', 'js', 'python'];
console.log(langs.indexOf('js'));

Answer 2

String.indexOf()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf

Array.indexOf()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf

JavaScript indexOf method: Explained with 5 examples to search in arrays
https://www.jquery-az.com/javascript-indexof-method-explained-with-6-examples-to-search-in-arrays/

Answer 3

Ali Tarek 👍You are welcome! 😊

Before asking a question on the Q/A,
try to search :

 • Google Advanced Search :
Set domain to 》sololearn.com《 for  search only on the SoloLearn
https://www.google.com/advanced_search

  • Eclipse Wiki :
"Before asking a question on the forums"
https://wiki.eclipse.org/Before_asking_a_question_on_the_forums

  • SoloLearn Advanced Search :
http://www.freecodeexamples.com/2018/12/sololearn-advanced-search.html

https://code.sololearn.com/W26q4WtwSP8W/?ref=app