Array Iterators

Mutates array

(Original Array) const fruits = ["Banana", "Orange", "Apple", "Mango"]
Example returns Modified Array Purpose
fruits.copyWithin(2, 0); ["Banana", "Orange", "Banana", "Orange"] copies array elements to another position in an array, overwriting the existing values.
fruits.fill("Kiwi"); ["kiwi", "kiwi", "kiwi", "kiwi"]  fills specified elements in an array with a static value.
fruits.push("Kiwi"); 5 ["Banana", "Orange", "Apple", "Mango", "Kiwi"] adds new items to the end of an array.
fruits.unshift("Lemon","Pineapple"); 6 [“Lemon”, “Pineapple”, "Banana", "Orange", "Apple", "Mango"];  adds new items to the beginning of an array, and returns the new length.
fruits.splice(2, 0, "Lemon", "Kiwi"); ["Banana", "Orange", “Lemon”, “Kiwi”, "Apple", "Mango"]; adds and/or removes array elements.
fruits.pop(); "Mango" ["Banana", "Orange", "Apple"]; removes the last element of an array
fruits.shift(); "Banana" ["Orange", "Apple", "Mango"];  removes the first item of an array.
fruits.sort(); ["Apple", "Banana", "Mango", "Orange" ];  sorts the elements of an array.
fruits.reverse(); ["Mango", "Apple", "Orange", "Banana"] reverses the order of the elements in an array.

Creates new Array

Example New Array(returned) Original Array Purpose function
hege.concat(stale); ["Emil", "Tobias", "Linus", "Cecilie", "Lone"]; const hege = ["Cecilie", "Lone"]; const stale = ["Emil", "Tobias", "Linus"]; joins two or more arrays.
Array.from("ABCDEFG"); [A,B,C,D,E,F,G] "ABCDEFG" Create an Array from a String
fruits.join() "Banana,Orange,Apple,Mango" const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns an array as a string. It behaves just like toString, but you can also specify the separator
fruits.toString(); "Banana,Orange,Apple,Mango" const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns a string with all array values separated by commas.
fruits.slice(1,3); ["Orange", "Lemon"]; const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"]; returns selected elements in an array, as a new array.
numbers.map(Math.sqrt) ; [2, 3, 4, 5] const numbers = [4, 9, 16, 25];  creates a new array with the results of calling a function for every array element.
ages.filter(checkAdult); [32, 33, 40] const ages = [32, 33, 16, 40]; ; creates an array filled with all array elements that pass a test (provided by a function). function checkAdult(age) {
     return age >= 18;
}

Extracts info

Example returns orignal array Purpose function
fruits.length; 4 const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns the number of elements in an array
fruits.includes("Mango") //true const fruits = ["Banana", "Orange", "Apple", "Mango"]; true if an array contains a specified element, otherwise false.
fruits.indexOf("Apple") 2 const fruits = ["Banana", "Orange", "Apple", "Mango"];  searches an array for a specified item and returns its position.
Array.isArray(fruits) //true const fruits = ["Banana", "Orange", "Apple", "Mango"];  returns true if an object is an array, otherwise false.
fruits.valueOf();  ["Banana", "Orange", "Apple", "Mango"] const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns the array itself.
fruits.lastIndexOf("Apple") 2 const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns the last index (position) of a specified value.
numbers.reduce(myFunc); 100 const numbers = [175, 50, 25]; executes a reducer function for each value of an array. function myFunc(total, num) { return total - num; }
numbers.reduceRight(myFunc) -200 const numbers = [175, 50, 25]; executes a reducer function for each value of an array , from right to left. function myFunc(total, num) { return total - num; }
ages.some(checkAdult) //true const ages = [3, 10, 18, 20]; checks if any of the elements in an array pass a test (provided as a function). function checkAdult(age) { return age >= 18; }
ages.every(checkAge) //false const ages = [32, 33, 16, 40];  returns true if all elements in an array pass a test (provided as a function). function checkAge(age) { return age > 18; }
ages.find(checkAge) 20 const ages = [3, 10, 18, 20]; returns the value of the array element that passes a test (provided by a function). function checkAge(age) { return age > 18; }
ages.findIndex(checkAge) 3 const ages = [2, 10, 18, 20]; returns the index of the first array element that passes a test (provided by a function). function checkAge(age) { return age > 18; }
fruits.entries(); [0, "Banana"] [1, "Orange"] [2, "Apple"] [3, "Mango"] const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns an Array Iterator object with key/value pairs. for (let x of f) {
     document.getElementById("demo").innerHTML += x;
}
fruits.keys() 0,1,2,3 const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns an Array Iterator object with the keys of an array. for (let x of keys) {
     text += x + "<br>";
}

Forward counting only for loop

Example returns Original Array Purpose function
fruits.forEach(myFunction); 0: apple 1: orange 2: cherry const fruits = ["apple", "orange", "cherry"]; calls a function once for each element in an array, in order. function myFunction(item, index) {
     text += index + ": " + item + "<br>";
}

allows you to add new properties and methods to Arrays or find out constructor of array.

Example returns Original Array Purpose function
fruits.constructor; function Array() { [native code] } const fruits = ["Banana", "Orange", "Apple", "Mango"]; returns the function that created the Array prototype.
fruits.myUcase(); BANANA,ORANGE,APPLE,MANGO const fruits = ["Banana", "Orange", "Apple", "Mango"]; add new properties and methods to Arrays. Array.prototype.myUcase = function() {
     for (let i = 0; i < this.length; i++) {
         this[i] = this[i].toUpperCase();
    }
  };