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JavaScript•Working with Data

JavaScript Array Search

Flash cards

Review the key moves

1/4

Core idea

What is the main idea behind JavaScript Array Search?

Lesson checks

Practice each idea before moving on

Short Mimo-style checks built from this lesson's code, terms, and sequence.

1Quick choice

Which statement best captures the main point of this lesson?

2Fill blank

Complete the missing token from the example code.

___ fruits = ["Apple", "Orange", "Apple", "Mango"];

3Order

Put the learning moves in the order that makes the concept easiest to apply.

JavaScript Array lastIndexOf()

JavaScript Array indexOf()

Array Search Methods

Array indexOf() Array lastIndexOf() Array includes()	Array find() Array findIndex() Array findLast() Array findLastIndex()

Complete JavaScript Array Reference

JavaScript Array indexOf()

The indexOf() method searches an array for an element value and returns its position.

Note

The first item has position 0, the second item has position 1, and so on.

Example

const fruits = ["Apple", "Orange", "Apple", "Mango"];
let position = fruits.indexOf("Apple") + 1;

Syntax

array
.indexOf(
item
,
 start
)

item	Required. The item to search for.
start	Optional. Where to start the search. Negative values will start at the given position counting from the end, and search to the end.

Array.indexOf() returns -1 if the item is not found.

If the item is present more than once, it returns the position of the first occurrence.

JavaScript Array lastIndexOf()

Array.lastIndexOf() is the same as Array.indexOf() , but returns the position of the last occurrence of the specified element.

Example

const fruits = ["Apple", "Orange", "Apple", "Mango"];
let position = fruits.lastIndexOf("Apple") + 1;

Syntax

array
.lastIndexOf(
item
,
 start
)

item	Required. The item to search for
start	Optional. Where to start the search. Negative values will start at the given position counting from the end, and search to the beginning

JavaScript Array includes()

ECMAScript 2016 introduced Array.includes() to arrays. This allows us to check if an element is present in an array (including NaN, unlike indexOf).

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.includes("Mango"); // is true

Syntax

array
.includes(
search-item
)

Array.includes() allows to check for NaN values. Unlike Array.indexOf().

Browser Support

includes() is an ECMAScript 2016 feature.

ES2016 is fully supported in all modern browsers since March 2017 :

Chrome 52	Edge 15	Firefox 52	Safari 10.1	Opera 39
Jul 2016	Apr 2017	Mar 2017	May 2017	Aug 2016

JavaScript Array find()

The find() method returns the value of the first array element that passes a test function.

This example finds (returns the value of) the first element that is larger than 18:

Example

const numbers = [4, 9, 16, 25, 29];
let first = numbers.find(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

Note that the function takes 3 arguments:

The item value
The item index
The array itself

Browser Support

find() is an ES6 feature .

ES6 is fully supported in all modern browsers since June 2017:

Chrome 51	Edge 15	Firefox 54	Safari 10	Opera 38
May 2016	Apr 2017	Jun 2017	Sep 2016	Jun 2016

JavaScript Array findIndex()

The findIndex() method returns the index of the first array element that passes a test function.

This example finds the index of the first element that is larger than 18:

Example

const numbers = [4, 9, 16, 25, 29];
let first = numbers.findIndex(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

Note that the function takes 3 arguments:

The item value
The item index
The array itself

Browser Support

findIndex() is an ES6 feature .

ES6 is fully supported in all modern browsers since June 2017:

Chrome 51	Edge 15	Firefox 54	Safari 10	Opera 38
May 2016	Apr 2017	Jun 2017	Sep 2016	Jun 2016

JavaScript Array findLast() Method

ES2023 added the findLast() method that will start from the end of an array and return the value of the first element that satisfies a condition.

Example

const temp = [27, 28, 30, 40, 42, 35, 30];
let high = temp.findLast(x => x > 40);

Browser Support

findLast() is an ECMAScript 2023 feature.

JavaScript 2023 is supported in all modern browsers since July 2023 :

Chrome 110	Edge 110	Firefox 115	Safari 16.4	Opera 96
Feb 2023	Feb 2023	Jul 2023	Mar 2023	May 2023

JavaScript Array findLastIndex() Method

The findLastIndex() method finds the index of the last element that satisfies a condition.

Example

const temp = [27, 28, 30, 40, 42, 35, 30];
let pos = temp.findLastIndex(x => x > 40);

Browser Support

findLastIndex() is an ECMAScript 2023 feature.

JavaScript 2023 is supported in all modern browsers since July 2023 :

Chrome 110	Edge 110	Firefox 115	Safari 16.4	Opera 96
Feb 2023	Feb 2023	Jul 2023	Mar 2023	May 2023

JavaScript Get Date Methods

JavaScript Set Logic

Loading lesson path

JavaScript•Working with Data

JavaScript Array Search

Flash cards

Review the key moves

1/4

Core idea

What is the main idea behind JavaScript Array Search?

Lesson checks

Practice each idea before moving on

Short Mimo-style checks built from this lesson's code, terms, and sequence.

1Quick choice

Which statement best captures the main point of this lesson?

2Fill blank

Complete the missing token from the example code.

___ fruits = ["Apple", "Orange", "Apple", "Mango"];

3Order

Put the learning moves in the order that makes the concept easiest to apply.

JavaScript Array lastIndexOf()

JavaScript Array indexOf()

Array Search Methods

Array indexOf() Array lastIndexOf() Array includes()	Array find() Array findIndex() Array findLast() Array findLastIndex()

Complete JavaScript Array Reference

JavaScript Array indexOf()

The indexOf() method searches an array for an element value and returns its position.

Note

The first item has position 0, the second item has position 1, and so on.

Example

const fruits = ["Apple", "Orange", "Apple", "Mango"];
let position = fruits.indexOf("Apple") + 1;

Syntax

array
.indexOf(
item
,
 start
)

item	Required. The item to search for.
start	Optional. Where to start the search. Negative values will start at the given position counting from the end, and search to the end.

Array.indexOf() returns -1 if the item is not found.

If the item is present more than once, it returns the position of the first occurrence.

JavaScript Array lastIndexOf()

Array.lastIndexOf() is the same as Array.indexOf() , but returns the position of the last occurrence of the specified element.

Example

const fruits = ["Apple", "Orange", "Apple", "Mango"];
let position = fruits.lastIndexOf("Apple") + 1;

Syntax

array
.lastIndexOf(
item
,
 start
)

item	Required. The item to search for
start	Optional. Where to start the search. Negative values will start at the given position counting from the end, and search to the beginning

JavaScript Array includes()

ECMAScript 2016 introduced Array.includes() to arrays. This allows us to check if an element is present in an array (including NaN, unlike indexOf).

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.includes("Mango"); // is true

Syntax

array
.includes(
search-item
)

Array.includes() allows to check for NaN values. Unlike Array.indexOf().

Browser Support

includes() is an ECMAScript 2016 feature.

ES2016 is fully supported in all modern browsers since March 2017 :

Chrome 52	Edge 15	Firefox 52	Safari 10.1	Opera 39
Jul 2016	Apr 2017	Mar 2017	May 2017	Aug 2016

JavaScript Array find()

The find() method returns the value of the first array element that passes a test function.

This example finds (returns the value of) the first element that is larger than 18:

Example

const numbers = [4, 9, 16, 25, 29];
let first = numbers.find(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

Note that the function takes 3 arguments:

The item value
The item index
The array itself

Browser Support

find() is an ES6 feature .

ES6 is fully supported in all modern browsers since June 2017:

Chrome 51	Edge 15	Firefox 54	Safari 10	Opera 38
May 2016	Apr 2017	Jun 2017	Sep 2016	Jun 2016

JavaScript Array findIndex()

The findIndex() method returns the index of the first array element that passes a test function.

This example finds the index of the first element that is larger than 18:

Example

const numbers = [4, 9, 16, 25, 29];
let first = numbers.findIndex(myFunction);
function myFunction(value, index, array) {
  return value > 18;
}

Note that the function takes 3 arguments:

The item value
The item index
The array itself

Browser Support

findIndex() is an ES6 feature .

ES6 is fully supported in all modern browsers since June 2017:

Chrome 51	Edge 15	Firefox 54	Safari 10	Opera 38
May 2016	Apr 2017	Jun 2017	Sep 2016	Jun 2016

JavaScript Array findLast() Method

ES2023 added the findLast() method that will start from the end of an array and return the value of the first element that satisfies a condition.

Example

const temp = [27, 28, 30, 40, 42, 35, 30];
let high = temp.findLast(x => x > 40);

Browser Support

findLast() is an ECMAScript 2023 feature.

JavaScript 2023 is supported in all modern browsers since July 2023 :

Chrome 110	Edge 110	Firefox 115	Safari 16.4	Opera 96
Feb 2023	Feb 2023	Jul 2023	Mar 2023	May 2023

JavaScript Array findLastIndex() Method

The findLastIndex() method finds the index of the last element that satisfies a condition.

Example

const temp = [27, 28, 30, 40, 42, 35, 30];
let pos = temp.findLastIndex(x => x > 40);

Browser Support

findLastIndex() is an ECMAScript 2023 feature.

JavaScript 2023 is supported in all modern browsers since July 2023 :

Chrome 110	Edge 110	Firefox 115	Safari 16.4	Opera 96
Feb 2023	Feb 2023	Jul 2023	Mar 2023	May 2023

JavaScript Get Date Methods

JavaScript Set Logic