find the index of the element in array

findIndex.js

var a = ['one', 'two', 'three'];

//what is the index of the element 'two'
var index = a
.map(function (el, index) {
  return {
    index: index,
    value: el
  };
})
.filter(function (el) { 
  return el.value === 'two'; 
})
.map(function (el) { 
  return el.index 
})[0];
console.log(index)