.map() with call back function

.map() accepts a callback function as one of its arguments, and an important parameter of that function is the current value of the item being processed by the function. This is a required parameter. With this parameter, we can modify each individual item in an array and create a new function off of it.

const numbers = [1,2,3,4,5];
const newNumbers = numbers.map(number => {
return number*2;
});
console.log(numbers); 
// will print [1,2,3,4,5]
console.log(newNumbers);
// will print [2,4,6,8,10]

Another way to to do this iteration

// create a function to use
const newNumbers = number => number * 2;

// we have an array
const numbers = [1, 2, 3, 4, 5];

// call the function we made. more readable
const numbers = numbers.map(newNumbers);

console.log(newNumbers); // [2, 4, 6, 8, 10]

Convert an string to array using map function

const name = "John"
const map = Array.prototype.map

const nameArray = map.call(name, eachLetter => {
    return eachLetter;
})

console.log(nameArray) // ["J", "o", "h", "n"]

Reformatting array object in Javascript using map function

const userLikes = [
    { name: 'shark', likes: 'ocean' },
    { name: 'turtle', likes: 'pond' },
    { name: 'otter', likes: 'fish biscuits' }
]

const userLikeAge = userLikes.map(user => {
    const container = {};

    container[user.name] = user.likes;
    container.age = user.name.length * 10;

    return container;
})


console.log(userLikeAge);
// [{shark: "ocean", age: 50}, {turtle: "pond", age: 60}, {otter: "fish biscuits", age: 50}]

Map function to iterate an Javascript object

var myObject = { 'a': 1, 'b': 2, 'c': 3 };

Object.keys(myObject).map((key, index) => {
  myObject[key] *= 2;
});

console.log(myObject);
// => { 'a': 2, 'b': 4, 'c': 6 }