const arr = ['node.js', 'php', 'python', 'c', 'c#', 'java'];
const fromIndex = arr.indexOf('c#');
const toIndex = 2;
const element = arr.splice(fromIndex, 1)[0];
arr.splice(toIndex, 0, element);
console.log(arr);
/*
run:
[ 'node.js', 'php', 'c#', 'python', 'c', 'java' ]
*/