add index in for loop js code example

Example 1: javascript enumerate with index

const iterable = [...];
for (const [index, elem] in iterable.entries()) {
  f(index, elem);
}

// or
iterable.forEach((elem, index) => {
  f(index, elem);
});

Example 2: javascript for loop return index

const targetindex = myarray.findIndex(item => item.name === 'xyz');