FosseryWeb

Get items of array

Return an item by index (starting from 0):

// array = [1, 2, 3, 4, 5, "Hello World", true, undefined];

console.log(array[0]); // prints 1 to the console
console.log(array[1]); // prints 2 to the console

Return index of an item (first occurrence) using indexOf(item) method (returns -1 if item is not found):

// array = [1, 2, 3, 4, 5, "Hello World", true, undefined];

console.log(array.indexOf("Hello World")); // prints 5 to the console because the item "Hello World" is found on index 5

Return the length of array using the length property (counts from 1):

// array = [1, 2, 3, 4, 5, "Hello World", true, undefined];

console.log(array.length); // array contains 8 items so it prints 8 to the console

Check if an item is in the array

Using includes(item) method:

// array = [1, 2, 3, 4, 5, "Hello World", true, undefined];

console.log(array.includes("Hello World")); // prints true to the console

Using includes(item) method with two arguments (second is starting index):

// array = [1, 2, 3, 4, 5, "Hello World", true, undefined];

console.log(array.includes("Hello World", 6)); // prints false to the console because it starts looking for "Hello World" from 7th element (true)

Modify an item

Modify an item on a specific index (indexes start from 0):

// array = [1, 2, 3, 4, 5, "Hello World", true, undefined];

array[6] = false; // the 7th item of array changes from true to false: [1, 2, 3, 4, 5, "Hello World", false, undefined]

Add items to the start or end of array

Add items to the start of array using unshift(item1, item2) method (can have limitless number of parameters):

// array = [1, 2, 3, 4, 5, "Hello World", false, undefined];

array.unshift("boiii", "gurl"); // array will contain the following items: ["boiii", "gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined]

Add items to the end of array using push(item1, item2) method (can have limitless number of parameters):

// array = ["boiii", "gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined];

array.push(NaN, null, "Bye World"); // array will contain the following items: ["boiii", "gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined, NaN, null, "Bye World"]

Remove a single item from the start or end of array

Remove first item of array using shift() method (also returns the removed item):

// array = ["boiii", "gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined, NaN, null, "Bye World"];

let removedFromStart = array.shift(); // removedFromStart stores the item "boiii" which is removed from array. Array will contain the following items: ["gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined, NaN, null, "Bye World"]

Remove last item of array using pop() method (also returns the removed item):

// array = ["gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined, NaN, null, "Bye World"];

let removedFromEnd = array.pop(); // removedFromEnd stores the item "Bye World" which is removed from array. Array will contain the following items: ["gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined, NaN, null]

Add or remove multiple items anywhere inside array

Remove items using splice(startingIndex, numberOfItemsToRemove) method (creates and returns a new array with removed items):

// array = ["gurl", 1, 2, 3, 4, 5, "Hello World", false, undefined, NaN, null];

let removedFromMiddle = array.splice(7, 4); // Removes 4 items starting from index 7 and stores them in removedFromMiddle: [false, undefined, NaN, null]. The original array will contain the following items: ["gurl", 1, 2, 3, 4, 5, "Hello World"]

Remove and add items at the same time using splice(startingIndex, numberOfItemsToRemove. itemToAdd1, itemToAdd2) method (there can be limitless number of itemToAdd parameters, creates and returns a new array with removed items):

// array = ["gurl", 1, 2, 3, 4, 5, "Hello World"];

let removedFromMiddle2 = array.splice(1, 5, 21, 69); // removes 5 items starting from index 1 and stores them in removedFromMiddle2: [1, 2, 3, 4, 5]. Then it adds the items 21 and 69 to the original array, also starting from index 1. The original array will contain the following items: ["gurl", 21, 69, "Hello World"]

(if you just want to add items without removing any, provide 0 to the second, numberOfItemsToRemove parameter)

Add items of array to another array

Spread operator:

// array = ["gurl", 21, 69, "Hello World"];

let array2 = ["Goodbye World", "See ya"];
array.push(...array2); // adds items of array2 to the end of array so array will contain the following items: ["gurl", 21, 69, "Hello World", "Goodbye World", "See ya"]

Iterate through the array

Iterate through the array using for loop:

// length starts from 1 and index from 0!
for (let i = 0; i < array.length; i++) {
  console.log(array[i]);
}
// prints the item in index i of array during each iteration

Using forEach(function(item){}) method:

array.forEach(function(item) {
  console.log(item);
});
// item parameter gets the value of next item during each iteration

// shorthand:

array.forEach(item => console.log(item));

function containsHelloWorld(array) {
  array.forEach(function(item) {
    if (item === "Hello World") {
      return true;
    }
  });
  return false;
}

function containsHelloWorld(array) {
  for (let i = 0; i < array.length; i++) {
    if (array[i] === "Hello World") {
      return true;
    }
  }
  return false;
}

Create a new array with modified version of items from original array using map(function(item){}) method:

// array = ["gurl", 21, 69, "Hello World", "Goodbye World", "See ya"];

let newArray = array.map(item => item + 1); // Adds 1 to each items of array and adds them to newArray. The original array remains untouched. Items of array: ["gurl", 21, 69, "Hello World", "Goodbye World", "See ya"] Items of newArray: ["gurl1", 22, 70, "Hello World1", "Goodbye World1", "See ya1"]

Check a statement against all items of array using every(function(item){}) method (returns true if all items match the statement, otherwise it returns false):

// array = ["gurl", 21, 69, "Hello World", "Goodbye World", "See ya"];

let allItemsAreNumbers = array.every(item => typeof item === "number"); // allItemsAreNumbers will be false because there are also some string items in array

Ordering items using sort() method (modifies original array)

Put string items into alphabetical order - case-sensitive:

let stringArray = ["Hello", "gurl", "boiii", "World"];
stringArray.sort(); // Result: ["Hello", "World", "boiii", "gurl"]. Uppercase comes first.

Put string items into reverse alphabetical order - case-sensitive:

// stringArray = ["Hello", "World", "boiii", "gurl"];

stringArray.sort().reverse(); // Result: ["gurl", "boii", "World", "Hello"]

Put string items into alphabetical order - case-insensitive:

// stringArray = ["gurl", "boii", "World", "Hello"];

stringArray.sort(function (a, b) {
  return a.toLowerCase()
    .localeCompare(b.toLowerCase());
});
// Result: ["boiii", "gurl", "Hello", "World"]

Put string items into reverse alphabetical order - case-insensitive:

// stringArray = ["boiii", "gurl", "Hello", "World"];

stringArray.sort(function (a, b) {
  return a.toLowerCase()
    .localeCompare(b.toLowerCase());
}).reverse();
// Result: ["World", "Hello", "gurl", "boiii"]

Put number items into ascending order:

let numberArray = [69, 18, 21, 180];
numberArray.sort((a, b) => a - b); // Result: [18, 21, 69, 180] (If you call sort() on numberArray without the (a, b) => a - b callback function it checks each digit of numbers separately so the result would be: [18, 180, 21, 69])

Put number items into descending order:

// numberArray = [18, 21, 69, 180];

numberArray.sort((a, b) => b - a); // Result: [180, 69, 21, 18]

Multidimensional array

let mdArray = [["Hello", "World"], ["Pretty", "Gurl", 69]];

Return and modify items of embedded arrays:

// mdArray = [["Hello", "World"], ["Pretty", "Gurl", 69]];

console.log(mdArray[1][2]); // Prints the index 2 item - 69 - of index 1 embedded array - ["Pretty", "Gurl", 69] - to the console

mdArray[0][0] = "Goodbye"; // Result: [["Goodbye", "World"], ["Pretty", "Gurl", 69]];

Use array methods:

// mdArray = [["Goodbye", "World"], ["Pretty", "Gurl", 69]];

mdArray[0].unshift("Oh");
mdArray[1].push(21);
let removed = mdArray[1].shift();
mdArray.push(["Let's", "Go"]);
// Result: [["Oh", "Goodbye", "World"], ["Gurl", 69, 21], ["Let's", "Go"]]

Iteration:

for (let i = 0; i < array.length; i++) {
  for (let j = 0; j < array[i].length; j++) {
    console.log(array[i][j]);
  }
} // during each iteration of inner for loop it prints the index j item of index i embedded array to the console

// or

array.forEach(function(nestedArray) {
  nestedArray.forEach(function(item) {
    console.log(item);
  });
});