Node functions in javascript

Node.js Tutorial — Node.js Functions

JavaScript is a functional programming language, functions are fully typed objects that can be manipulated, extended, and passed around as data.

A normal function structure in JavaScript is defined as follows.

All functions return a value in JavaScript.

In the absence of an explicit return statement, a function returns undefined.

 function myData() < return 123; >console.log(myData()); // 123 function myValue() < >console.log(myValue()); // undefined 

Example

The following code shows how to create a function:

 function hello(name) < console.log("hello " + name); > hello("CSS"); 

The code above generates the following result.

Note

To declare parameters for a function in JavaScript, list them in the parentheses.

There is no checking of these parameters at runtime:

 function hello(name) < console.log("hello " + name); > hello(); hello("CSS", "HTML", "AAA", 4); 

The code above generates the following result.

If too few parameters are passed into a function call, the resulting variables are assigned the value undefined.

If too many are passed in, the extras are simply unused.

All functions have a predefined array in the body called arguments .

It has all the values that were passed in to the function, and we can do extra checking on the parameter list.

Functions in JavaScript do not even need to have names:

 var x = function (a, b) < return a + b; >console.log(x(10, 20)); 

The code above generates the following result.

The nameless functions are typically called anonymous functions.

Function Scope

Every time a function is called, a new variable scope is created.

Variables declared in the parent scope are available to that function.

Variables declared within the new scope are not available when the function exits.

Consider the following code:

 var pet = 'cat'; function myMethod() < var pet = 'dog'; console.log(pet); > myMethod(); console.log(pet); 

The code above generates the following result.

Combining this scoping with anonymous functions is better way to use private variables that will disappear when the anonymous function exits.

Example 2

Here’s a contrived example to compute the volume of a cone:

 var height = 5; var radius = 3; var volume; // declare and immediately call anonymous function to create scope (function () /*from w w w . j av a 2 s . c o m*/ var pir2 = Math.PI * radius * radius; // temp var volume = (pir2 * height) / 3; >)(); console.log(volume); 

The code above generates the following result.

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Node.js функция

В JavaScript функция в качестве параметра другой функции принимает. Мы можем определить функцию, а затем перейти к быть определены непосредственно в передаточной функции место.

Node.js использовать функцию, аналогичную функции Javascript, например, вы можете сделать это:

function say(word) < console.log(word); >function execute(someFunction, value) < someFunction(value); >execute(say, "Hello");

Приведенный выше код, мы говорим, что функция в качестве первого аргумента выполнять функции были переданы. Это возвращение не возвращаемое значение, скажем, но сказать, себя!

Таким образом, говорят, становится выполнение локальных переменных SomeFunction, выполнить с помощью вызова SomeFunction () (в виде скобок), чтобы сказать, использование функции.

Конечно, так как говорят, есть переменная, выполнение может передать такую ​​переменную при вызове SomeFunction.

функция Anonymous

Мы можем поставить функцию, переданную в качестве аргумента. Но мы не должны об этом «впервые определены, а затем передать,» круг, мы можем определить другую функцию в скобках и передать эту функцию:

function execute(someFunction, value) < someFunction(value); >execute(function(word)< console.log(word) >, "Hello");

Мы принимаем первый аргумент в выполнение непосредственно определяет, где мы готовы передать для выполнения функции.

Таким образом, мы не даже имя для этой функции, поэтому она называется анонимной функцией.

Функция передачи, как получить работу HTTP-сервера

С этим знанием, мы смотрим на наш простой, но не простой сервер HTTP:

var http = require("http"); http.createServer(function(request, response) < response.writeHead(200, ); response.write("Hello World"); response.end(); >).listen(8888);

Теперь он выглядит намного должно быть ясно: мы передаем анонимную функцию к функции createServer.

Такой код может также достичь той же цели:

var http = require("http"); function onRequest(request, response) < response.writeHead(200, ); response.write("Hello World"); response.end(); > http.createServer(onRequest).listen(8888);

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Learn All About Node.js Functions

Node.js is JavaScript running on the server. It is an open-source, cross-platform, back-end JavaScript runtime environment that executes JavaScript code outside a web browser.

Basics to Advanced — Learn It All!

What Is a Function?

A function is a logical set of statements summoned to get the desired result or perform a specific action.

Functions in Node.js are used directly in the code. Using Node.js functions enables you to get the desired action of your app in a single process, i.e., you don’t have to create a new thread for every new request.

Function Scope

A new variable scope gets created whenever you call a function.

It raises two different scenarios:

Consider the below sample code:

Code Output:

Following is the output you will get when the above code runs:

Combining scoping with anonymous functions is a better way to use private variables; the variables disappear when you exit the anonymous function.

Create New Node.js Function

Creating functions in Node.js is not different from creating processes in JavaScript. You can create a new Node.js function to get the desired output by following the steps discussed below.

1. First, you have to click on the Workflows option from your Node.js main window. It will navigate you to your Workflow Dashboard.

2. From the upper taskbar, click on the Functions tab.

3. Post this, a new page will pop up, from where you have to click on the New Function button. A create page will appear asking for required inputs.

4. Now, enter a Function Name; remember that this name will be the identifier to invoke the function. Make sure the function name has no empty spaces and should be meaningful.

5. In the language choice, select Node.js for scripting your function.

6. As per your requirement, specify the Arguments.

7. Click on the Create Function button; clicking this will bring the builder to your screen.

8. Lastly, you need to add the required Node.js code to your created function.

To check if your function is created or not, visit the Functions section in the workflow dashboard.

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Arguments and Parameters

Arguments and Parameters are among the essential parts of a function. Arguments are the instances passed to the method, and Parameters are the variables assigned to store value for the arguments.

You can specify an argument directly along with the Node.js function during function creation.

But, what if there is a requirement to add more arguments? If you want to add more arguments for the same function, you can easily do so using the FunctionProperties option available on the builder page.

It’s important to define parameters used in the Node.js functions before running your program.

If you find the parameter to be confusing, remember it’s like a container that receives the argument value after getting passed from the deluge.

Sample Function

Node.js has different functions for different uses like any other programming language, for example, Sample Function. You can create Sample Function whenever you find the necessity to calculate the average in Node.js.

Sample Function, when implemented, uses deluge and receives values obtained to update records.

Call a Node.js Function

Calling a function in Node.js is quite similar to calling a function in Java.

Check out the statement in the code below to call a Node.js function in a deluge script.

In this example, the Node.js function “thisapp.calculatorFunction(total,count);” contains the total value as a collection and prints when called.

Basics to Advanced — Learn It All!

Get Value

The Get Value Node.js function assigns variables to the parameters (Parameters that you input in the arguments to obtain your desired output).

The two parameters used in the above code, Total (Grand Total) and Count (Number of Subjects), can be easily obtained using the command statement basicIO.getParameter.

To upload the .js format file, you need to use the node_modules folder. You can directly use this folder in your Node.js functions code.

The folder allows you to create the code and save it. Also, you can directly use your Node.js function whenever you need to access this code.

Key Notes:

• Return Type: A Node.js function always gives a Collection data type value in return.
• Namespace: Node.js has a default Namespace: «Namespace».
• Argument: Always use string argument in Node.js functions because it accepts only string values.
• You cannot rename your Node.js functions it is created.

Learn More About Node.js Today!

Ryan Dahl introduced Node.js in 2009. This function can be used to build scalable network applications such as command-line applications, web applications, real-time chat applications, REST API servers, etc. Node.js is widely used for building network programs like web servers, similar to PHP, Java, or ASP.NET.

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About the Author

Ravikiran A S

Ravikiran A S works with Simplilearn as a Research Analyst. He an enthusiastic geek always in the hunt to learn the latest technologies. He is proficient with Java Programming Language, Big Data, and powerful Big Data Frameworks like Apache Hadoop and Apache Spark.

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