Javascript function as array element

JavaScript Arrays

An array is a special variable, which can hold more than one value:

Why Use Arrays?

If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

An array can hold many values under a single name, and you can access the values by referring to an index number.

Creating an Array

Using an array literal is the easiest way to create a JavaScript Array.

It is a common practice to declare arrays with the const keyword.

Learn more about const with arrays in the chapter: JS Array Const.

Example

Spaces and line breaks are not important. A declaration can span multiple lines:

Example

You can also create an array, and then provide the elements:

Example

Using the JavaScript Keyword new

The following example also creates an Array, and assigns values to it:

Example

The two examples above do exactly the same.

There is no need to use new Array() .

For simplicity, readability and execution speed, use the array literal method.

Accessing Array Elements

You access an array element by referring to the index number:

Note: Array indexes start with 0.

[0] is the first element. [1] is the second element.

Changing an Array Element

This statement changes the value of the first element in cars :

Example

Converting an Array to a String

The JavaScript method toString() converts an array to a string of (comma separated) array values.

Example

const fruits = [«Banana», «Orange», «Apple», «Mango»];
document.getElementById(«demo»).innerHTML = fruits.toString();

Access the Full Array

With JavaScript, the full array can be accessed by referring to the array name:

Example

Arrays are Objects

Arrays are a special type of objects. The typeof operator in JavaScript returns «object» for arrays.

But, JavaScript arrays are best described as arrays.

Arrays use numbers to access its «elements». In this example, person[0] returns John:

Array:

Objects use names to access its «members». In this example, person.firstName returns John:

Object:

Array Elements Can Be Objects

JavaScript variables can be objects. Arrays are special kinds of objects.

Because of this, you can have variables of different types in the same Array.

You can have objects in an Array. You can have functions in an Array. You can have arrays in an Array:

Array Properties and Methods

The real strength of JavaScript arrays are the built-in array properties and methods:

Array methods are covered in the next chapters.

The length Property

The length property of an array returns the length of an array (the number of array elements).

Example

The length property is always one more than the highest array index.

Accessing the First Array Element

Example

Accessing the Last Array Element

Example

Looping Array Elements

One way to loop through an array, is using a for loop:

Example

const fruits = [«Banana», «Orange», «Apple», «Mango»];
let fLen = fruits.length;

You can also use the Array.forEach() function:

Example

const fruits = [«Banana», «Orange», «Apple», «Mango»];

Adding Array Elements

The easiest way to add a new element to an array is using the push() method:

Example

const fruits = [«Banana», «Orange», «Apple»];
fruits.push(«Lemon»); // Adds a new element (Lemon) to fruits

New element can also be added to an array using the length property:

Example

const fruits = [«Banana», «Orange», «Apple»];
fruits[fruits.length] = «Lemon»; // Adds «Lemon» to fruits

Adding elements with high indexes can create undefined «holes» in an array:

Example

const fruits = [«Banana», «Orange», «Apple»];
fruits[6] = «Lemon»; // Creates undefined «holes» in fruits

Associative Arrays

Many programming languages support arrays with named indexes.

Arrays with named indexes are called associative arrays (or hashes).

JavaScript does not support arrays with named indexes.

In JavaScript, arrays always use numbered indexes.

Example

const person = [];
person[0] = «John»;
person[1] = «Doe»;
person[2] = 46;
person.length; // Will return 3
person[0]; // Will return «John»

WARNING !!
If you use named indexes, JavaScript will redefine the array to an object.

After that, some array methods and properties will produce incorrect results.

Example:

const person = [];
person[«firstName»] = «John»;
person[«lastName»] = «Doe»;
person[«age»] = 46;
person.length; // Will return 0
person[0]; // Will return undefined

The Difference Between Arrays and Objects

In JavaScript, arrays use numbered indexes.

In JavaScript, objects use named indexes.

Arrays are a special kind of objects, with numbered indexes.

When to Use Arrays. When to use Objects.

• JavaScript does not support associative arrays.
• You should use objects when you want the element names to be strings (text).
• You should use arrays when you want the element names to be numbers.

JavaScript new Array()

JavaScript has a built-in array constructor new Array() .

But you can safely use [] instead.

These two different statements both create a new empty array named points:

These two different statements both create a new array containing 6 numbers:

The new keyword can produce some unexpected results:

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Passing Array to Function in JavaScript

Similar to C/C++/Java, we can pass the entire array as a parameter to a function in JavaScript. This method of array passing is called call by reference in JavaScript.

To pass an array argument to a function, simply pass the name of an array (a reference to an array) without brackets.

For example, if we have declared an array marks as:

let hourlyTemp = new Array(30);

then function call statement:

passes array hourlyTemp to the function modifyArray(). JavaScript automatically passes arrays to functions using call-by-reference (or passed by reference).

Function Receiving an Array via Function Call

For a function to receive an array via a function call, you must specify a parameter in the function’s parameter list that will refer to the array in the function body.

Unlike other programming languages, JavaScript does not hand over any specific syntax for this purpose. JavaScript simply needs that the name of an array to be specified in the function parameter list.

For example, we can write the function definition for the function modifyArray as:

The above function definition indicates that modifyArray() receives an array of integers in parameter x (the argument supplied in the calling function must be an array).

When the called function uses the array name x, it points to the original array in the caller (array hourlyTemp).

Therefore, when the called function updates any array elements in its function body, it is updating the actual elements of the array in their original memory locations.

Passing Array to Function as Pass by Reference

1. Let’s create a JavaScript program in which we will pass an initialized array to a function. Then, we will multiply each array element by 5 and display it.

Output: Original array elements are: 20 10 25 15 35 40 Modified array elements: 100 50 125 75 175 200

In this example program, we have passed an array nums into modifyArray() as pass by reference. That is, the parameter nums is passed into modifyArray() function with reference to x. Inside the function the array elements are multiplied by 5 and displayed.

Output: Original array elements are: 10 20 30 40 50 Modified array elements are: 20 40 60 80 100

Passing Individual Array Element to Function as Pass by Value

Let’s create a JavaScript program in which we will pass the entire array as a pass by reference to the function in JavaScript. Then we will pass the individual array element to the function as a pass by value in JavaScript.

Program code 3:

Output: Original array: 10 20 30 40 50 Modified array: 40 80 120 160 200 nums[3] before modifyElement: 160 nums[3] after modifyElement: 480

Although the entire array is passed by reference, whereas individual numeric and boolean array elements are passed by value.

To pass an element of an array to a function, use the sub-scripted name of the element as an argument value in the function call.

In this tutorial, you learned an interesting topic “passing array to function in JavaScript” with many example programs. Hope that you will have understood how to pass an individual element of an array in JavaScript.
Thanks for reading.
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