part4.md

JavaScript Fundamentals - Part 4

Arrays

JavaScript arrays are used to store multiple values in a single variable. Arrays are objects and the typeof operator returns "object".

Array Methods

W3schools covers some of the most useful built-in array methods.

• The splice() method can be used to add new items to an array.

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 0, "Lemon", "Kiwi");
// or
fruits.splice(0, 1);        // Removes the first element of fruits

• The slice() method creates a new array. It does not remove any elements from the source array.

The Arguments Object

Arguments is an Array-like object accessible inside functions that contains the values of the arguments passed to that function. The arguments object is a local variable available within all non-arrow functions. You can refer to a function's arguments inside that function by using its arguments object. It has entries for each argument the function was called with, with the first entry's index at 0.

As you can do with any Array-like object, you can use the Array.from() method or spread syntax to convert arguments to a real Array:

let args = Array.from(arguments);
// or
let args = [...arguments];

Rest Parameters

The rest parameter syntax allows us to represent an indefinite number of arguments as an array.

// Spread syntax (...)
function sum(...theArgs) {
  return theArgs.reduce((previous, current) => {
    return previous + current;
  });
}

console.log(sum(1, 2, 3));
// expected output: 6

console.log(sum(1, 2, 3, 4));
// expected output: 10

forEach Method

var removeFromArray = function(...args) {
    let newArr = [];
    const array = args[0];
    
    // array.forEach(func) – func is executed by forEach for every array item.    
    array.forEach((item) => {
        if (!args.includes(item)) {
             newArr.push(item);
             };
             });
             return newArr;
             };

console.log(removeFromArray([1, 2, 3, 4, 5, 7, 8], 1, 4, 8));