Javascript Functions

Functions that allow us to structure our code into smaller and more reusable units.

When we write a program, we often need to perform the same action in many places. For example, we want to show a message to the users when they complete an action.

To avoid repeating the same code all over places, we can use a function to wrap that code and reuse it. We can these function as many times as needed.

There are many built-in functions such as alert() and console.log() provided by javascript.

Advantages of Functions

Following are the advantages of using functions in our code:-

• Code reusability: We can call a function several times so it save coding.
• Less coding: It makes our program compact. We don’t need to write many lines of code each time to perform a common task.

Function Syntax

To declare a function, we will start with function keyword followed by function name, and then parentheses (). Following is the syntax to use it:-

Syntax:-

Input:-

These function name can contain letters, digits, underscores and dollar signs  and it must be a valid JavaScript identifier. By convention, the function name should start with a verb like getData(), fetchContents(), or isValid().

Function Arguments

Arguments are the different parameters which we can pass within a function parenthesis.

A function can accept zero, one, or multiple parameters. If there are multiple parameters, we need to separate them by commas (,). Inside the function , the arguments (the parameters) behave as local variables.

Syntax:-

Input:-

These function name can contain letters, digits, underscores and dollar signs  and it must be a valid JavaScript identifier. By convention, the function name should start with a verb like getData(), fetchContents(), or isValid().

Invocation function

When we call a function, the function executes the code inside its body. This process is also known as invocation. To call a function, we use its name followed by the function arguments enclosed in parentheses.

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Function with return value

Return statement is required to stop execution of any function and control the value it should return. Every function in JavaScript returns undefined, unless otherwise specified.

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Function Object

The purpose of function is to create a new Function object. It executes the code globally.

Inside the body of a function, we can access an object called arguments that represents the named arguments of the function.

For example, we can use the square bracket [] to access the arguments: arguments[0] returns the first argument, arguments[1] returns the second one, and so on.

Furthermore, we can use the length property of the arguments object to determine the number of arguments.

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In the above example, getSum() function will take multiple arguments and output the sum out of it.

Function Hoisting

Function hoisting is a concept to use a function before it is declared. It is a mechanism that the JavaScript engine physically moves function declarations to the top of the code before executing them.

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Function methods

Following are the function methods which can be used within a code:-