Js Array Common Method 1

1. Join

The join() method 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.

JavaScript

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"

2. reverse

The reverse() method reverses an array in place. The first array element becomes the last, and the last array element becomes the first.

Reverse is destrutive

JavaScript

const array1 = ['one', 'two', 'three'];
console.log('array1:', array1);
// expected output: "array1:" Array ["one", "two", "three"]

const reversed = array1.reverse();
console.log('reversed:', reversed);
// expected output: "reversed:" Array ["three", "two", "one"]

// Careful: reverse is destructive -- it changes the original array.
console.log('array1:', array1);
// expected output: "array1:" Array ["three", "two", "one"]

3. sort

The sort() method sorts the elements of an array in place and returns the sorted array. The default sort order is ascending, built upon converting the elements into strings, then comparing their sequences of UTF-16 code units values.

The time and space complexity of the sort cannot be guaranteed as it depends on the implementation.

JavaScript

const months = ['March', 'Jan', 'Feb', 'Dec'];
months.sort();
console.log(months);
// expected output: Array ["Dec", "Feb", "Jan", "March"]

const array1 = [1, 30, 4, 21, 100000];
array1.sort();
console.log(array1);
// expected output: Array [1, 100000, 21, 30, 4]

Parameters

compareFunction Optional

Specifies a function that defines the sort order. If omitted, the array elements are converted to strings, then sorted according to each character's Unicode code point value.

• If compareFunction(a, b) returns a value > than 0, sort b before a.

• If compareFunction(a, b) returns a value < than 0, sort a before b.

• If compareFunction(a, b) returns 0, a and b are considered equal.

JavaScript

var numbers = [4, 2, 5, 1, 3];
numbers.sort(function(a, b) {
  return a - b;
});
console.log(numbers);

// [1, 2, 3, 4, 5]

Use arrow function expressions with shorter syntax

JavaScript

let numbers = [4, 2, 5, 1, 3];
numbers.sort((a, b) => a - b);
console.log(numbers);

// [1, 2, 3, 4, 5]

4. Push / Pop and Shift / Unshift

The push() method adds one or more elements to the end of an array and returns the new length of the array.

The pop() method removes the last element from an array and returns that element. This method changes the length of the array.

The shift() method removes the first element from an array and returns that removed element. This method changes the length of the array. The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.

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5. find

The find() method returns the value of the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.

JavaScript

const array1 = [5, 12, 8, 130, 44];

const found = array1.find(element => element > 10);

console.log(found);
// expected output: 12