Javascript get elements by index

How do I reference an array item by its index in JavaScript?

I see you’re using an object, but want to use indices as well. As @Edgar Villegas Alvarado mentions, this is not a native feature.

4 Answers 4

It looks like you are confusing JavaScript array objects with the fact that all objects are associative arrays. Note that normal objects (e.g. the «Fruit» object you allude to) do not have an intrinsic ordering of properties (keys) whereas Array objects do (due to the natural ordering of integral indices). Essentially, an Array is just an object with a special «length» property that stores the last integer index (starting from zero) plus one.

Any object’s properties will be iterated in arbitrary (e.g. random) order:

var obj = ; for (var prop in obj) < alert(prop + '=' + obj[prop]); // No order is guaranteed. >

Strictly speaking, even arrays are not guaranteed by the specification to iterate in natural order using a for-in loop; however, most JavaScript interpreters do so anyway. (Notably, IE8 iterates in the order that indices were assigned, not natural order.) This is why you should always iterate arrays using indices in a plain «for» loop.

var arr = ['a', 'b', 'c', 'd', 'e', 'f']; for (var i=0; i 

These differences mean that regardless of how your «Fruit» object is defined there is no reliable way to ensure a strict ordering of keys (e.g. «Banana», «Apple», «Color», «Size», etc.) unless you retain your own ordering separately.

Ok this is good, I can get «Colour», «Size» and «Cost» how do I then get their values also? like a for loop in a for loop or something?

@Craig: see my updated answer: try using obj[prop] where prop is the iterator variable in a for. in loop.

@maerics — the properties (numeric or otherwise) of arrays aren’t ordered either. Arrays are just objects with a special length property.

@RobG: yes, that’s true about Array objects and the ECMA-262 5th Edition specification states that the order of enumerated properties is not specified; however, in every JavaScript interpreter I’ve used, arrays will iterate in-order in a for-in loop.

@maerics—add array properties out of order in IE, then do a for..in loop. The are returned in the order they were added, not numeric (in IE < 9 at least).

I’m a little confused, because you seem to have answered your own question. I also don’t know how you have your array(s) set up. But if you take a look at this example, you can see it working here:

This assumes that the top level array contains your fruit types and second level array contains each fruit type’s properties.

In JavaScript 1.0, you can refer to an object’s properties by their property name or by their ordinal index. In JavaScript 1.1 or later, however, if you initially define a property by its name, you must always refer to it by its name, and if you initially define a property by an index, you must always refer to it by its index.

So the issue is that you declare an associative array, instead of an indexed/ordinal-based one. The only solution I can think of is using a (ugly) for loop. Here’s some un-tested pseudo-code:

function getItemByIndex(index, array) < var counter = 0; for (item in array) < if (counter == index) < return item; >counter++; > > 

I guess the array would look like: Fruit = [Banana => [Colour => ‘Yellow’, Size => ‘Large’, Cost => ‘$3.50’], Apple=> [Colour => ‘Green’, Size => ‘Small’, Cost => ‘$0.42’]];

@Kon mutating native objects should be discouraged. It can cause issues with other libraries (see PrototypeJs as an example of a troublesome library). Instead I’d suggest using wrappers or passing both the array and the sought attribute in, like Dojo and YUI.

@Josh, I agree. I also was questioning that last point and actually removed it before seeing your comment. 🙂

You can’t, unless you copy your string indexes to numeric indexes, but they would be new elements in your array

You don’t indicate how you create your array or assign those values, but it sounds like you don’t know the difference between a JavaScript array and a JavaScript object.

An object has properties with keys that are strings, but you can’t access those properties with an index integer, only by the key.

An array is a special type of object that provides array functionality like a length property and some methods like sort() , etc. Array properties are normally assigned with numeric indexes, and the length property is based on those numerically indexed properties, but because arrays are still objects you can also assign properties with string keys. If you say myArray[‘banana’] = .. that ‘banana’ property is not accessible via an index number.

If you want keys like ‘banana’ you shouldn’t be using an array at all, just use a plain object.

Источник

Javascript: Get element of array by index

While working in javascript, often there is a requirement to delete an element from an array by index. This article will discuss accessing an element from the javascript array by an index value.

Get an array element by index using [ ]

Get the value of element at 3 rd index position in array [1,4,9,16,25]

let numArray = [1,4,9,16,25]; var value = numArray[3]; console.log(value);

Frequently Asked:

Note that the arrays have zero-based index .

Get the value of element at 2 nd index position in array [“Javascript”, “Is”, “Popular”, “Language”]

let stringArray = ["Javascript", "Is", "Popular","Language"]; var value = stringArray[2]; console.log(value);

I hope this article helped you to get an element from an array by index position in javascript. Good Luck .

Related posts:

Share your love

Leave a Comment Cancel Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Terms of Use

Disclaimer

Copyright © 2023 thisPointer

To provide the best experiences, we and our partners use technologies like cookies to store and/or access device information. Consenting to these technologies will allow us and our partners to process personal data such as browsing behavior or unique IDs on this site and show (non-) personalized ads. Not consenting or withdrawing consent, may adversely affect certain features and functions.

Click below to consent to the above or make granular choices. Your choices will be applied to this site only. You can change your settings at any time, including withdrawing your consent, by using the toggles on the Cookie Policy, or by clicking on the manage consent button at the bottom of the screen.

The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network.

The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.

The technical storage or access that is used exclusively for statistical purposes. The technical storage or access that is used exclusively for anonymous statistical purposes. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you.

The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes.

Источник

JavaScript Array Get by Index: A Comprehensive Guide to Accessing Elements

Learn how to access elements in JavaScript array by index using various techniques and methods such as bracket notation, indexOf(), find(), findIndex(), forEach() and map() method.

• JavaScript Arrays and Index Basics
• The indexOf() Method
• The find() Method
• The findIndex() Method
• The forEach() Method
• The map() Method
• Other examples of quickly accessing elements in a JavaScript array by index
• Conclusion
• How to get array value by index in JavaScript?
• How to get an element from array in JavaScript?
• How do you access an index in an array?
• How to get first index of array in JavaScript?

JavaScript is one of the most popular programming languages worldwide, and one of its core functionalities is arrays. Arrays are used to store multiple values in a single variable. accessing elements in a javascript array by index is a common task that can be achieved using various methods and techniques. In this blog post, we will provide a comprehensive guide on how to get or access elements in a JavaScript array by index, including key points, important points, and helpful points.

JavaScript Arrays and Index Basics

JavaScript arrays store elements as standard object properties using the array index. The first item in a JavaScript array has an index of zero. To get the value at a specific index in an array, use bracket notation: array[index] . For example, let’s say we have an array of fruits:

let fruits = ["Apple", "Banana", "Mango"]; 

To access the second element of this array, which is “Banana”, we can use bracket notation as follows:

console.log(fruits[1]); // Output: Banana 

The indexOf() Method

The indexOf() method returns the first index of a specified value in an array or -1 if the value is not found. For instance, let’s say we have an array of fruits:

let fruits = ["Apple", "Banana", "Mango"]; 

To find the index of “Mango” in this array, we can use the indexOf() method as follows:

console.log(fruits.indexOf("Mango")); // Output: 2 

The find() Method

The find() method is an iterative method that calls a provided callback function once for each element in an array in ascending-index order. It returns the first element in the array that satisfies the provided testing function. For instance, let’s say we have an array of numbers:

We can use the find() method to find the first number greater than 25 as follows:

let result = numbers.find(function(number) < return number >25; >); console.log(result); // Output: 30 

The findIndex() Method

The findIndex() method executes a function for each array element and returns the index of the first element that passes the function’s test. For example, let’s say we have an array of numbers:

We can use the findIndex() method to find the index of the first number greater than 25 as follows:

let result = numbers.findIndex(function(number) < return number >25; >); console.log(result); // Output: 2 

The forEach() Method

The forEach() method calls a provided callback function once for each element in an array in ascending-index order. For example, let’s say we have an array of numbers:

We can use the forEach() method to loop through the array and print each element as follows:

numbers.forEach(function(number)< console.log(number); >); // Output: 10 20 30 40 

The map() Method

The map() method creates a new array with the results of calling a provided function on every element in the array. For example, let’s say we have an array of numbers:

We can use the map() method to double each element in the array as follows:

let result = numbers.map(function(number)< return number * 2; >); console.log(result); // Output: [2, 4, 6, 8] 

Other examples of quickly accessing elements in a JavaScript array by index

In Javascript as proof, js get element by index code example

var arr = ["item", "item2"]; arr.indexOf("item"); // return 0 arr.indexOf("item2") //retrun 1

In Javascript , in particular, js array code sample

var colors = [ "red", "orange", "yellow", "green", "blue" ]; //Arrayconsole.log(colors); //Should give the whole array console.log(colors[0]); //should say "red" console.log(colors[1]); //should say "orange" console.log(colors[4]); //should say "blue"colors[4] = "dark blue" //changes "blue" value to "dark blue" console.log(colors[4]); //should say "dark blue" //I hope this helped :)

In Javascript as proof, get array element by index javascript code example

var firstArrayItem = myValues[0] 

Conclusion

Accessing elements in a JavaScript array by index is a common task that can be achieved using various methods and techniques. Key points include using bracket notation and understanding the basics of javascript arrays and index. Important points include the use of other methods such as lastIndexOf(), slice(), at(), and keys() method. Helpful points include understanding the advantages and disadvantages of using javascript arrays and best practices such as initializing them with the correct length and using the Array.isArray() method to check if a variable is an array. By using the methods discussed in this blog post, you can easily access elements in a JavaScript array by index and perform various operations on them.

Источник