map()
Creates a new array populated with the results of calling a provided function on every element in the calling array.
const arr = [1, 2, 3, 4, 5, 6];
// add one to every element
const oneAdded = arr.map(num => num + 1);
console.log(oneAdded);
// output [2, 3, 4, 5, 6, 7]
console.log(arr);
// output: [1, 2, 3, 4, 5, 6]
Another Sample:
const 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]
forEach()
Executes a provided function once for each array element.Help you to loop over array’s items.
const arr = [1, 2, 3, 4, 5, 6];
arr.forEach(item => {
console.log(item);
// output: 1 2 3 4 5 6
});
Another Sample:
const array1 = ['a', 'b', 'c'];
array1.forEach(element => console.log(element));
// expected output: "a"
// expected output: "b"
// expected output: "c"
includes()
Determines whether an array includes a certain value among its entries, returning true or false as appropriate.
const arr = [1, 2, 3, 4, 5, 6];
arr.includes(2); // output: true
arr.includes(7); // output: false
Another Sample:
const array1 = [1, 2, 3];
console.log(array1.includes(2));
// expected output: true
const pets = ['cat', 'dog', 'bat'];
console.log(pets.includes('cat'));
// expected output: true
console.log(pets.includes('at'));
// expected output: false
filter()
Creates a new array with all elements that pass the test implemented by the provided function
Creates an array filled with all array elements that pass a test (provided as a function)
const arr = [1, 2, 3, 4, 5, 6];
// item(s) greater than 3
const filtered = arr.filter(num => num > 3);
console.log(filtered); // output: [4, 5, 6]
console.log(arr); // output: [1, 2, 3, 4, 5, 6]
Another Sample:
const words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];
const result = words.filter(word => word.length > 6);
console.log(result);
// expected output: Array ["exuberant", "destruction", "present"]
reduce()
Executes a reducer function (that you provide) on each element of the array, resulting in single output value.
const arr = [1, 2, 3, 4, 5, 6];
const sum = arr.reduce((total, value) => total + value, 0);
console.log(sum);
// 21
Another Sample:
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
some()
Tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value.
const arr = [1, 2, 3, 4, 5, 6];
// at least one element is greater than 4?
const largeNum = arr.some(num => num > 4);
console.log(largeNum); // output: true
// at least one element is less than or equal to 0?
const smallNum = arr.some(num => num <= 0);
console.log(smallNum);
// output: false
Another Sample:
const array = [1, 2, 3, 4, 5];
// checks whether an element is even
const even = (element) => element % 2 === 0;
console.log(array.some(even));
// expected output: true
every()
Tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value. If passed, it return true otherwise false.
const arr = [1, 2, 3, 4, 5, 6];
// all elements are greater than 4
const greaterFour = arr.every(num => num > 4);
console.log(greaterFour); // output: false
// all elements are less than 10
const lessTen = arr.every(num => num < 10);
console.log(lessTen); // output: true
Another Sample:
const isBelowThreshold = (currentValue) => currentValue < 40;
const array1 = [1, 30, 39, 29, 10, 13];
console.log(array1.every(isBelowThreshold));
// expected output: true
join()
Creates and returns a new string by concatenating all of the elements in an array (or an array-like object), separated by commas or a specified separator string. If the array has only one item, then that item will be returned without using the separator.
const elements = ['Fire', 'Air', 'Water'];
console.log(elements.join());
// expected output: "Fire,Air,Water"
console.log(elements.join(''));
// expected output: "FireAirWater"
console.log(elements.join('-'));
// expected output: "Fire-Air-Water"
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