Array Helper Methods are very helpful when you need to manipulate your data stored in arrays. They make life much easier, so we should know them.

forEach Helper

The forEach() function is used to iterates through all the entries of the array.

ES5 Example:

var colors = ['red','blue','green'];

<script>
colors.forEach(function(color){
    console.log(color);
});
</script>

Output:

red
blue
green

ES6 Example:

<script>
colors.forEach(color => {
    console.log(color);
});
</script>

Every Helper

The every() method tests whether all elements in the array pass the test implemented by the provided function, example: Check if all the values in the computers array are 16 or over:

Example:

const computers = [
  { name: 'Apple', ram: 24 },
  { name: 'Compaq', ram: 4 },
  { name: 'Acer', ram: 32 }
];

<script>
computers.every(computer => {
    return computer.ram > 16;
});
</script>

Output:

false

This returned false since not all the computer.ram values are greater than 16.

Some Helper

And the some() method tests whether any values in the computers array are 16 or over:

Example:

const computers = [
  { name: 'Apple', ram: 24 },
  { name: 'Compaq', ram: 4 },
  { name: 'Acer', ram: 32 }
];

<script>
computers.some(computer => {
    return computer.ram > 16;
});
</script>

Output:

true

This returned true because we have at least one computer.ram value that is greater than 16.

Filter Helper

Filters the list of fruits for those:

Example:

const products = [
  { name: 'cucumber', type: 'vegetable', quantity: 0, price: 1 },
  { name: 'banana', type: 'fruit', quantity: 10, price: 15 },
  { name: 'celery', type: 'vegetable', quantity: 30, price: 13 },
  { name: 'orange', type: 'fruit', quantity: 3, price: 5 }
];

<script>
let totalFruits = products.filter(fruit => {
    return product.type === 'fruit';
});
</script>

This will return all the products that are type fruit, in this case banana and orange.

Map Helper

The map() method is used to iterate through all the entries of the array, modifies them and returns a new array but the old array is not manipulated. Take in mind that the return keyword is mandatory.

Example:

const numbers = [1,2,3];

<script>
let doubled = numbers.map(number => {
    return number * 2;
});
</script>

Output:

console.log(numbers):
(3) [1, 2, 3]
console.log(doubled):
(3) [2, 4, 6]

Reduce Helper

The reduce() method is used to compact all values in an array down to a single value.

This is a very basic example:

const bill = [39.85, 42.99, 49.99];

<script>
const sum = bill.reduce((total, amount) => {
    return total + amount;
});
</script>

Output:

132.83