How to Find the JavaScript Array Length

The length property of a JavaScript array returns the number of elements in the array, providing an easy way to determine its size. It's dynamic, meaning it updates as elements are added or removed, and can also be set explicitly to truncate or clear the array. This property is fundamental for iterating over arrays and managing their contents efficiently. 

The array’s length, or the number of values in the array, is something you’ll frequently want to know. The JavaScript array length property comes into the role, it's one of the methods of JavaScript. The length property returns how many elements are contained in a specific array.

Let us take the example of a vendor who wants to know how many boxes are there in stock. Using the JavaScript array length property, he can find out how many boxes are available in the warehouse. In this blog, we will learn how to find the length of Javascript array using this property.

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Table of Contents

• JavaScript Array Length
• Modification in JavaScript Array Length Property
• Iterating Through an Array
• Shortening an Array
• Make an Array of Void

JavaScript Array Length

The JavaScript array length property is an integer value representing the quantity of items in an array. Since index values in JavaScript begin at 0, the length property is always one more than the highest index value in the array. The length property of an array, is a 32-bit unsigned integer that is always numerically greater than the array’s highest index.

The JavaScript property length does not accept any parameters because it is a property. It adds a new item at the end of an array.

The syntax for the JavaScript property for array length is as follows:

We append the.length syntax to the end of the array’s name to access the length property’s value.

Example:

// expected output:

4

Explanations:

Array Declaration: The cars array is declared with four elements: 'Mercedes', 'BMW', 'Audi', and 'MG Hector'.

Length Property: cars.length refers to the length property of the cars array. This property calculates the number of elements in the array.

Output: When console.log(cars.length); is executed, it prints 4 to the console. This number represents the total count of elements in the cars array, which in this case are four car brands.

The length property is a straightforward way to find out how many items are stored in an array, which is especially useful for looping through arrays or performing operations on their contents.

Modification in JavaScript Array Length

The array object observes the length property, automatically synchronizing the length value and array content. The array length property’s value can be changed in JavaScript. You can empty the array of elements or make it sparse by adjusting the length value. This implies:

• In case the length is set to a value lower than the current value, any elements beyond that are removed from the array.
• Any index greater than 232 extends the array; the length property is updated to reflect the new maximum index.
• RangeError exception is thrown when the length is set to an invalid value, such as a negative number or a non-integer.
• When the length is set to a number greater than the current length, empty slots are added rather than actual undefined items.

The following example shows the length property to iterate across the array numbers. Then, each element’s value is doubled.

1. Iterating Through an Array

Output:

// numbers is now [2, 4, 6, 8, 10]

Explanation:

Array Initialization:

The numbers array is initialized with the elements [1, 2, 3, 4, 5].

Getting Array Length:

const length = numbers.length; stores the length of the numbers array (which is 5) in the length variable.
Looping Through the Array:

1. The for loop is set up to iterate over the array. It starts with i = 0 and runs as long as i is less than length (5 in this case).
2. On each iteration, i is incremented by 1 (i++).
Modifying Array Elements:

1. Inside the loop, each element of the array is accessed using numbers[i] and then multiplied by 2.
2. The result of this multiplication replaces the original value at that position in the array (numbers[i] *= 2).
Result:

After the loop completes, each original number in the array has been doubled.
Therefore, the numbers array is transformed into [2, 4, 6, 8, 10].

2. Shortening an Array

If the current length is more than 3, the next example reduces the array to a length of 2. 

Output:

[4,9]

Explanation:
1. The numbers array is correctly initialized with multiple number elements: [4, 9, 16, 25, 36].
2. By setting numbers.length = 2, the array is truncated, keeping only the first two elements (4 and 9) and discarding the rest.
3. When console.log(numbers); is executed, it prints the truncated array [4, 9], showing the result of this operation.

3. Make an Array of Void

The array is empty if the length is set to 0:

Output:

[]

Explanation:

Array Initialization:

The numbers array is initialized with three string elements: '4', '9', and '16'.
Setting Array Length to 0:

The line numbers.length = 0; sets the length of the numbers array to 0. This operation effectively removes all elements from the array, making it empty.
Output:

1. The console.log(numbers); statement then outputs the current state of the numbers array.
2. Since the array has been emptied, the output is [], indicating an empty array.

Conclusion

The length of a JavaScript array returns the number of elements that are kept in a list. This approach is beneficial when figuring averages and other calculations when knowing the y is necessary.

The number of items in a JavaScript array may be found using the length property covered in this tutorial. Additionally, two examples of the length characteristic were discussed. You can use the length property like a pro after reading this guide!