No mutation
The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.
Array.prototype.concat ( [ item1 [ , item2 [ , … ] ] ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat
var array1 = ['a', 'b', 'c']; var array2 = ['d', 'e', 'f']; console.log(array1.concat(array2)); // expected output: Array ["a", "b", "c", "d", "e", "f"]
The copyWithin() method shallow copies part of an array to another location in the same array and returns it, without modifying its size.
arr.copyWithin(target) arr.copyWithin(target, start) arr.copyWithin(target, start, end)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/copyWithin
var array1 = ['a', 'b', 'c', 'd', 'e']; // copy to index 0 the element at index 3 console.log(array1.copyWithin(0, 3, 4)); // expected output: Array ["d", "b", "c", "d", "e"] // copy to index 1 all elements from index 3 to the end console.log(array1.copyWithin(1, 3)); // expected output: Array ["d", "d", "e", "d", "e"]
The entries() method returns a new Array Iterator object that contains the key/value pairs for each index in the array.
a.entries()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/entries
var array1 = ['a', 'b', 'c']; var iterator1 = array1.entries(); console.log(iterator1.next().value); // expected output: Array [0, "a"] console.log(iterator1.next().value); // expected output: Array [1, "b"]
The every() method tests whether all elements in the array pass the test implemented by the provided function.
Array.prototype.every ( callbackfn [ , thisArg ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every
function isBelowThreshold(currentValue) { return currentValue < 40; } var array1 = [1, 30, 39, 29, 10, 13]; console.log(array1.every(isBelowThreshold)); // expected output: true
The fill() method fills all the elements of an array from a start index to an end index with a static value.
arr.fill(value) arr.fill(value, start) arr.fill(value, start, end)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/fill
var array1 = [1, 2, 3, 4]; // fill with 0 from position 2 until position 4 console.log(array1.fill(0, 2, 4)); // expected output: [1, 2, 0, 0] // fill with 5 from position 1 console.log(array1.fill(5, 1)); // expected output: [1, 5, 5, 5] console.log(array1.fill(6)); // expected output: [6, 6, 6, 6]
The filter() method creates a new array with all elements that pass the test implemented by the provided function.
Array.prototype.filter ( callbackfn [ , thisArg ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
var words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present']; const result = words.filter(word => word.length > 6); console.log(result); // expected output: Array ["exuberant", "destruction", "present"]
The find() method returns a value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.
arr.find(callback[, thisArg])
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find
var array1 = [5, 12, 8, 130, 44]; var found = array1.find(function(element) { return element > 10; }); console.log(found); // expected output: 12
The findIndex() method returns an index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.
arr.findIndex(callback[, thisArg])
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex
var array1 = [5, 12, 8, 130, 44]; function isLargeNumber(element) { return element > 13; } console.log(array1.findIndex(isLargeNumber)); // expected output: 3
The forEach() method executes a provided function once per array element.
Array.prototype.forEach ( callbackfn [ , thisArg ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach
var array1 = ['a', 'b', 'c']; array1.forEach(function(element) { console.log(element); }); // expected output: "a" // expected output: "b" // expected output: "c"
The includes() method determines whether an array includes a certain element, returning true or false as appropriate.
arr.includes(searchElement) arr.includes(searchElement, fromIndex)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes
var array1 = [1, 2, 3]; console.log(array1.includes(2)); // expected output: true var pets = ['cat', 'dog', 'bat']; console.log(pets.includes('cat')); // expected output: true console.log(pets.includes('at')); // expected output: false
The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present.
Array.prototype.indexOf ( searchElement [ , fromIndex ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf
var beasts = ['ant', 'bison', 'camel', 'duck', 'bison']; console.log(beasts.indexOf('bison')); // expected output: 1 // start from index 2 console.log(beasts.indexOf('bison', 2)); // expected output: 4 console.log(beasts.indexOf('giraffe')); // expected output: -1
The join() method joins all elements of an array into a string.
Array.prototype.join (separator)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join
var elements = ['Fire', 'Wind', 'Rain']; console.log(elements.join()); // expected output: Fire,Wind,Rain console.log(elements.join('')); // expected output: FireWindRain console.log(elements.join('-')); // expected output: Fire-Wind-Rain
The keys() method returns a new Array Iterator that contains the keys for each index in the array.
arr.keys()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/keys
var array1 = ['a', 'b', 'c']; var iterator = array1.keys(); for (let key of iterator) { console.log(key); // expected output: 0 1 2 }
The lastIndexOf() method returns the last index at which a given element can be found in the array, or -1 if it is not present. The array is searched backwards, starting at fromIndex.
Array.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/lastIndexOf
var animals = ['Dodo', 'Tiger', 'Penguin', 'Dodo']; console.log(animals.lastIndexOf('Dodo')); // expected output: 3 console.log(animals.lastIndexOf('Tiger')); // expected output: 1
The map() method creates a new array with the results of calling a provided function on every element in this array.
Array.prototype.map ( callbackfn [ , thisArg ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map
var array1 = [1, 4, 9, 16]; // pass a function to map const map1 = array1.map(x => x * 2); console.log(map1); // expected output: Array [2, 8, 18, 32]
The pop() method removes the last element from an array and returns that element. This method changes the length of the array.
Array.prototype.pop ( )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/pop
var plants = ['broccoli', 'cauliflower', 'cabbage', 'kale', 'tomato']; console.log(plants.pop()); // expected output: "tomato" console.log(plants); // expected output: Array ["broccoli", "cauliflower", "cabbage", "kale"] plants.pop(); console.log(plants); // expected output: Array ["broccoli", "cauliflower", "cabbage"]
The push() method adds one or more elements to the end of an array and returns the new length of the array.
Array.prototype.push ( [ item1 [ , item2 [ , … ] ] ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push
var animals = ['pigs', 'goats', 'sheep']; console.log(animals.push('cows')); // expected output: 4 console.log(animals); // expected output: Array ["pigs", "goats", "sheep", "cows"] animals.push('chickens'); console.log(animals); // expected output: Array ["pigs", "goats", "sheep", "cows", "chickens"]
The reduce() method applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value.
Array.prototype.reduce ( callbackfn [ , initialValue ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce
const array1 = [1, 2, 3, 4]; const reducer = (accumulator, currentValue) => accumulator + currentValue; // 1 + 2 + 3 + 4 console.log(array1.reduce(reducer)); // expected output: 10 // 5 + 1 + 2 + 3 + 4 console.log(array1.reduce(reducer, 5)); // expected output: 15
The reduceRight() method applies a function against an accumulator and each value of the array (from right-to-left) has to reduce it to a single value.
Array.prototype.reduceRight ( callbackfn [ , initialValue ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/ReduceRight
const array1 = [[0, 1], [2, 3], [4, 5]].reduceRight( (accumulator, currentValue) => accumulator.concat(currentValue) ); console.log(array1); // expected output: Array [4, 5, 2, 3, 0, 1]
The reverse() method reverses an array in place. The first array element becomes the last, and the last array element becomes the first.
Array.prototype.reverse ( )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reverse
var array1 = ['one', 'two', 'three']; console.log('array1: ', array1); // expected output: Array ['one', 'two', 'three'] var reversed = array1.reverse(); console.log('reversed: ', reversed); // expected output: Array ['three', 'two', 'one'] /* Careful: reverse is destructive. It also changes the original array */ console.log('array1: ', array1); // expected output: Array ['three', 'two', 'one']
The shift() method removes the first element from an array and returns that element. This method changes the length of the array.
Array.prototype.shift ( )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/shift
var array1 = [1, 2, 3]; var firstElement = array1.shift(); console.log(array1); // expected output: Array [2, 3] console.log(firstElement); // expected output: 1
The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.
Array.prototype.slice (start, end)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice
var animals = ['ant', 'bison', 'camel', 'duck', 'elephant']; console.log(animals.slice(2)); // expected output: Array ["camel", "duck", "elephant"] console.log(animals.slice(2, 4)); // expected output: Array ["camel", "duck"] console.log(animals.slice(1, 5)); // expected output: Array ["bison", "camel", "duck", "elephant"]
The some() method tests whether some element in the array passes the test implemented by the provided function.
Array.prototype.some ( callbackfn [ , thisArg ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some
var array = [1, 2, 3, 4, 5]; var even = function(element) { // checks whether an element is even return element % 2 === 0; }; console.log(array.some(even)); // expected output: true
The sort() method sorts the elements of an array in place and returns the array. The sort is not necessarily stable. The default sort order is according to string Unicode code points.
Array.prototype.sort (comparefn)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort
var months = ['March', 'Jan', 'Feb', 'Dec']; months.sort(); console.log(months); // expected output: Array ["Dec", "Feb", "Jan", "March"] var array1 = [1, 30, 4, 21]; array1.sort(); console.log(array1); // expected output: Array [1, 21, 30, 4]
The splice() method changes the content of an array by removing existing elements and/or adding new elements.
Array.prototype.splice (start, deleteCount [ , item1 [ , item2 [ , … ] ] ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice
var months = ['Jan', 'March', 'April', 'June']; months.splice(1, 0, 'Feb'); // inserts at 1st index position console.log(months); // expected output: Array ['Jan', 'Feb', 'March', 'April', 'June'] months.splice(4, 1, 'May'); // replaces 1 element at 4th index console.log(months); // expected output: Array ['Jan', 'Feb', 'March', 'April', 'May']
The toLocaleString() method returns a string representing the elements of the array. The elements are converted to Strings using their toLocaleString methods and these Strings are separated by a locale-specific String (such as a comma “,”).
Array.prototype.toLocaleString ( )
var array1 = [1, 'a', new Date('21 Dec 1997 14:12:00 UTC')]; var localeString = array1.toLocaleString('en', {timeZone: "UTC"}); console.log(localeString); // expected output: "1,a,12/21/1997, 2:12:00 PM", // This assumes "en" locale and UTC timezone - your results may vary
The toSource() method returns a string representing the source code of the array.
arr.toSource()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toSource
The toString() method returns a string representing the specified array and its elements.
Array.prototype.toString ( )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toString
var array1 = [1, 2, 'a', '1a']; console.log(array1.toString()); // expected output: "1,2,a,1a"
The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.
Array.prototype.unshift ( [ item1 [ , item2 [ , … ] ] ] )
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/unshift
var array1 = [1, 2, 3]; console.log(array1.unshift(4, 5)); // expected output: 5 console.log(array1); // expected output: Array [4, 5, 1, 2, 3]
The values() method returns a new Array Iterator object that contains the values for each index in the array.
arr.values()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/values
const array1 = ['a', 'b', 'c']; const iterator = array1.values(); for (const value of iterator) { console.log(value); // expected output: "a" "b" "c" }
#javascript #arrays