findIndex.js

const lang = ["Java", "JavaScript"];
 
let hasJavaScript = function(currentElement, index, array){
  console.log(`currentElement = ${currentElement}`);
  console.log(`index = ${index}`);
  console.log("-------------------------");
  return array[index] === "JavaScript";
}
// element found in 1st index 
lang.findIndex( hasJavaScript ); // 1 

// output
currentElement = Java
index = 0
-------------------------
currentElement = JavaScript
index = 1
-------------------------
1