Javascript array of objects length

How to count JavaScript array objects?

In this tutorial, we will learn to count JavaScript array objects. The array is the data structure containing the strings, numbers, objects, etc., in JavaScript. The object is the one kind of entity that contains properties and methods related to it. We can access the object’s properties and invoke the object method using the object’s references.

Generally, To find the array length, we can use the array.length() method and it returns the total number of elements that the array includes. But what if we need to count only object elements?

Here, this tutorial has various approaches to counting the total number of object elements in the JavaScript array.

Using the for Loop and instanceof Operator

In this approach, we will use the for loop to count the total number of objects in the array. Users can iterate through every element of the array and check the type of every element using the instanceof operator. They can initialize the length variable with 0 to store a total number of objects. While iterating through the array elements, if they find any entity of type object, they can increase the length by 1.

Syntax

Users can use the syntax below to use for loop and instanceof operator to count array objects.

let objectsLen = 0; for (let i = 0; i < myArr.length; i++) < // if entity is object, increase objectsLen by 1, which is the stores the total number of objects in array. if (myArr[i] instanceof Object) < objectsLen++; >>

Algorithm

• STEP 1 − Create a variable named objectsLen and initialized it with 0.
• STEP 2 − Create an array and add some objects with other elements.
• STEP 3 − To count the number of objects in the array, we iterate through the array using for loop and check for the element type using the instanceof operator
• STEP 4 − If we find an entity of object type, we will add 1 to the objectsLen variable.
• STEP 5 − At last, we will print the objectsLen variable, which is the total number of objects.

Example

In the example below, count the total number of objects in an array. We use for loop to iterate through the array and apply instanceof operator to check the type of the array element.

   
Count JavaScript array objects.
 
Counting total number of array objects in array using the for loop. 
    

Using the array.filter() Method

In JavaScript, array.filter() method is used to filter the elements of the array. Users can add the callback function to the method and add some filtering conditions in the callback function. The filtering condition to filter all objects is to check for the element type in our case. Users can check for the type of the object using the typeof operator and return true from the callback function if the entity is a type of object. Otherwise, return false.

The array.filter() method returns the array of all filtered values. So, we will get the array of all objects, and we can measure its length using the .length() method.

Syntax

Users can follow the below syntax for the array.filter() method to count the number of objects.

// filter all entity which type is object let allObject = array.filter((val) => < // checking the type of elements using the typeof operator. if ( typeofval == 'object' ) < return true; >else < return false; >>); LettotalObjects = allObject.length;

Parameters

• array − It is an array of elements that contains the objects’ entities with other elements.
• val − It is an element of the array for which, the user wants to check the type and filter it if the entity is an object.

Example

In the example below, we have used the array.filter() method to filter all objects from the given array. At last, we have calculated the length of the object array, which is returned by the array.filter() method.

   
Count JavaScript array objects.
 
Counting total number of array objects in array using the arrays.filter() method.
    

Users have learned to calculate the object entities in a JavaScript array. The first approach and second approach have the same time complexity. When we take a look at the space complexity of both approaches first approach has lower space complexity and is optimized in a better way.

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How to Get the Length of an Object in JavaScript?

An object is a collection of key values linked as links between names and values. It is important to understand how to check the length of an object in order to avoid unnecessary bugs. Checking the object length in javascript isn’t a common and fundamental operation; however, it is crucial to understand how to do so. There is no default length property on the object. It is only available to arrays and strings that have the length property.

Introduction

Objects are collections of key-value pairs that have properties that are linked by their names. Understanding how to find the object’s length is not a common and basic operation, but in order to avoid unnecessary bugs, it is essential to know how it can be done. There is no length property by default on the object. It is only available to arrays and strings that have the length property. A JavaScript object’s length can be determined by either using one of its static methods or by using the for. in loop method. Let us explore them one by one

Method 1: Using the Object.keys() Method

An object’s length can be obtained by calling the Object.keys() method and accessing the length property, such as Object.keys(obj).length . A given object’s key name is returned by Object.keys(); its length is returned by its length property.

This example shows how we can find the length of an object with three fields using Object.keys().

Method 2: How to Loop through All the Fields of the Object and Check Their Property

A boolean value is returned by the hasOwnProperty() method indicating whether the specified property belongs to the object. It is possible to check whether each key is present within the object by using this method. Each key in the object is looped through, and if it is present, the total number of keys is increased. In this way, you can find out the object’s length from this.

This example shows how we can loop through the object with three fields using the hasOwnProperty() method. We loop through all the 3 fields inside the user and display it as output using hasOwnProperty() method.

Get Length of Object with Object.values()

The Object.values() method returns a list of the enumerable property values associated with the object. As a next step, we will use the object’s length property to determine how many elements there are in the array (length of the object).

This example shows how we can find the length of an object with three fields using Object.values() .

Get Length of Object with Object.entries()

The Object.entries() method returns a collection of string-keyed properties Javascript array of objects length on your object. We will then use the length property to determine the number of elements.

This example shows how we can find the length of an object with three fields using Object.entries().

Get Length of Object Using for…in Loop

In the for. in statement, all enumerable properties of an object, including inherited enumerable properties, are iterated over (ignoring ones keyed by symbols).

This example shows how we can find the length of an object with three fields using for..in the loop.

Object.keys vs Object.getOwnPropertyNames

The Object.getOwnPropertyNames() method returns the names of all the properties owned by an object. The Object.keys() method returns all the object’s enumerable properties. If you don’t set enumerable: false to any property, both return the same result.

The student object has two properties, including its name and age.

Let’s define another property named Class but set it to enumerable: false:

In JavaScript, a property is enumerable if it can be read while being iterated using the for. in the loop or the Object. keys() function.

Object.keys do not include the resolution property:

Object Length with Symbols

The symbol primitive data type was introduced in ECMAScript 6. It returns an array of all symbol properties found directly on an object using the getOwnPropertySymbol() method.

This example shows how we can find the length of an object with three fields using getOwnPropertySymbol() method.

Conclusion

1. We explored about the various ways we could use to find the length of objects using Object.values() , Object.entries() and by using for..in loop
2. The length property of the Object.keys() method is perhaps the simplest and fastest way to obtain the length of an object in JavaScript.
3. Both static and for..in loop would do the job for you but most programmers prefer the object static method only
4. Finding the length of javascript objects is not as easy as finding the length for arrays it is quite complicated but can be solved by using the methods listed in this article

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JavaScript: определяем количество элементов в объекте

В этой статье мы поговорим, как определить число элементов в JavaScript-объекте. Заодно посмотрим, как определяют количество элементов в массиве. И, разумеется, приведём практические примеры.

Как известно, люди нередко ищут сложные пути для решения достаточно простых задач. Так и здесь: определить количество элементов в массиве или объекте, по сути, несложно. Об этом и поговорим.

Итак, давайте представим, что у нас есть объект:

 
var myObject = new Object(); myObject["firstname"] = "Лев"; // Имя myObject["lastname"] = "Толстой"; // Фамилия myObject["age"] = 21; // Возраст 
 
И возникает закономерный вопрос: каким образом лучше рассчитать величину объекта, то есть количество входящих в него элементов? Смотрите, если подсчёт будет осуществляться в современных браузерах, то самый простой способ — следующий:
 
 
var size = Object.keys(myObject).length; 
 
Если же вам нужно обеспечить поддержку старых браузеров, может, пригодится и немного другой вариант:
 
 
// Функция, определяющая величину объекта Object.size = function(obj)  var size = 0, key; for (key in obj)  if (obj.hasOwnProperty(key)) size++; > return size; >; // В переменной size будет содержаться количество элементов объекта var size = Object.size(myObject); 
 
В принципе, ничего сложного нет. Давайте закрепим этот небольшой урок: 1. Если надо определить число элементов в массиве JavaScript:
 
 
//Определяем массив var arr = ["elem_1", "elem_2", "elem_3", "elem_4", "elem_5"]; //Узнаём число элементов массива, применяем к нему свойство length var countElementsArr = arr.length; //Распечатываем результат в консоль console.log(countElementsArr); 
 
2. Если надо определить число элементов в объекте JavaScript: 
 
 
//Определяем объект var obj = "first_name": "Ivan", "last_name": "Ivanov", "city": "Ivanovo", "country": "Russia">; //Узнаём число элементов объекта var countElementsObj = Object.keys(obj).length; //Распечатываем результат в консоль console.log(countElementsObj); 
 
 
https://wordpressrus.ru/javascript/javascript-opredelenie-razmera-massiva-i-obekta.html
 
https://wppw.ru/vo/kak-opredelit-kolichestvo-elementov-v-obekte-javascript
 
 
Если же интересуют не базовые знания, а действительно продвинутые навыки по разработке на JavaScript, записывайтесь на наши курсы:
 
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