(Javascript) How do you ignore lower/upper case being registered in search bars when searching for a specific item -

i tasked constructing search engine website displays various pictures have different titles. ie, "pictures of birds", "flying birds", "green birds". of when type in "birds" first 2 results display.
how can ignore case sensitive searches, when user types in "birds" 3 searches come up.

i hear converting string uppercase/lowercase ignore it. however, unfamiliar how implement this.
of have line of code within function:

var str = document.getelementbyid('searchtxt').value;  var upper = str.touppercase(); console.log(str); 

i trying print value in variable console. nothing working , on console 2 objects defined.
if explain need code functioning, i'd grateful.

you logging unconverted string console.

console.log(upper); 

should trick