There are three keywords in JavaScript that can be used to declare variables: let, var, and const. Each keyword has different rules and implications for how the variables they create can be used.

1. let: The let keyword declares a block-scoped local variable, optionally initializing it to a value.

   Block-scoped means that the variable is only available within the block it was declared in, which is usually denoted by curly braces {}.

2. var: The var keyword declares a function-scoped or global variable, optionally initializing it to a value.

   Function-scoped means that the variable is only available within the function it was declared in. Global variables are available throughout your entire code.

3. const: The const keyword declares a block-scoped, immutable constant variable, i.e. a variable that can’t be reassigned.

   Constants are also called “immutable variables”, but that’s a bit of a misnomer since they are actually variables – just ones that can’t be reassigned.

What is difference between var, let and const?

The var keyword is the oldest way of declaring variables in JavaScript and is supported by all browsers. The let and const keywords are newer additions to the language and are not supported by older browsers.

If you need to support older browsers, you can use var instead of let or const. If you don’t need to support older browsers, you can use let or const. If you want your variable to be immutable, use const.

Here are some examples:

var x = 1;
let y = 2;
const z = 3;

x = 4; //OK 
y = 5; //OK 
z = 6; //Error

As you can see, var and let variables can be reassigned, but const variables can not.

Another difference between var and let/const is that var variables are function-scoped, while let and const variables are block-scoped.

This means that var variables are only available within the function they were declared in. For example:

function foo() {
  var x = 1;
}

foo();
console.log(x); // ReferenceError: x is not defined

On the other hand, let and const variables are only available within the block they were declared in. For example:

function foo() {
  let y = 2;
  const z = 3;
}

foo();
console.log(y); // ReferenceError: y is not defined 
console.log(z); // ReferenceError: z is not defined

So, to sum up, the main differences between var, let and const are:

• var is function-scoped while let and const are block-scoped.
• var variables can be reassigned while let and const variables can not.
• var variables are declared using the var keyword while let and const variables are declared using the let and const keywords respectively.
• const variables are immutable while let and var variables are not.

The post What is difference between var, let and const in JavaScript? appeared first on TecAdmin.

Syntax:

string.replace(old_string, new_string)

Replace String in JavaScript with Examples

In this tutorial, we will discuss a few examples of replacing strings in Javascript.

Let’s try some examples:

• Here is the first example to initialize a text in a variable, then replace it with another text.

  let str = "Hello World!"
  let result = str.replace("World", "TecAdmin")
  
  console.log(result)

  Run the above example and see the results. Thanks to playcode.io that help me to run javascript online.

  

• What happens if a given string is found multiple times. In that case, the replace() function will replace the first occurrence of the given string.

  let str = "Mr Bean has a green Apple and a Red Apple"
  
  let result = str.replace("Apple", "Strawberries")
  
  console.log(result)

  Execute the above code and see the results:

  

  The result clearly shows that the first occurrence is replaced with a new string, but the second occurrence is not replaced. So, how can I replace all the occurrences of a given string? Let’s check the next example:

• We can also define the regular expression and the function will replace all occurrences matching that regular expression.

  See the below example, where we defined a regular expression to replace string globally.

  let str = "Mr Bean has a green Apple and a red Apple"
  
  const regex = "/Apple/ig"
  let result = str.replace("Apple", "Strawberries")
  
  console.log(result)

  Run the above example and see the results.

  

• Basically, the regular expression is used to match patterns. To replace all occurrences of any string, we can use replaceAll() function.

  The below example uses the replaceAll() function in javascript.

  let str = "Mr Bean has a green Apple and a red Apple"
  
  let result = str.replaceAll("Apple", "Strawberries")
  
  console.log(result)

  Run the above code and see the results.

  

Wrap Up

In this tutorial, we have discussed a few examples to replace a string in javascript.

The post How to Replace String in JavaScript appeared first on TecAdmin.

JavaScript Program to Add Two Numbers

In this JavaScript program, we will calculate the sum of two numbers and print the results on the console. Here we will use the common + sign to add numbers.

// define variable with integers
var num1 = 3;
var num2 = 2;

// add two numbers
var sum = num1 + num2;

// Show the results
console.log('The sum is: ' + sum);

Run the above example:

Here we have defined two variables with static integer values. Then calculate the sum of both values and store them in a third variable. Finally, the result is displayed on the console.

Another Example with User Input

Let’s consider another example to calculate the sum of values based on user input. First, have a look at the below program.

// Take user input
var x = window.prompt("Enter first number: ");
var y = window.prompt("Enter second number: ");

// Convert string to integer
var num1 = parseInt(x);
console.log('First input numer: ' + num1)

var num2 = parseInt(y);
console.log('Second input numer: ' + num2)

// Calcualte the Sum
var sum = num1 + num2;

// Show the results
console.log('The sum of ' + num1 + ' + ' + num2 + ' is: ' + sum);

See the result of the above example:

This program takes input from user. Here the window.prompt() function create a popuop box in browser to accept input. This input is in string format. So next, we use parseint() function to convert a string value to a integer.

Finally, calculate the sum of both integers and print the results. This time the results will be shown in a popup box.

The post JavaScript Program to Add Two Numbers appeared first on TecAdmin.

This tutorial described to you to remove duplicate array elements using JavaScript.

Example

Here is a sample JavaScript program to declare a static array with few default elements. Add some duplicate elements as well. After that, remove all the duplicate array elements.

// An example JavaScript program to remove duplicate values from an array

function returnUnique(value, index, self) {
  return self.indexOf(value) === index;
}

// usage example:
var arr = ['Green', 'Red', 100, 'Green', 20, '100'];
var unique = arr.filter(returnUnique);

console.log(unique); //

Output:

["Green", "Red", 100, 20, "100"]

In the above example, the value “Green” was defined twice in the array. As a result, you see only one instance of Green.

You may be thinking about element 100. Here the first occurrence of the element 100 is an integer value and the second one is defined as a string. In short, both elements are treated as unique.

The post JavaScript Program to Remove Duplicate Array Elements appeared first on TecAdmin.

Reference: Serve Node.js Application behind the Apache Server

Step 1 – Install Node.js

First of all, you need to install node.js on your system. Use the following commands to configure node.js PPA in your Debian system and install it.

sudo apt-get install software-properties-common
curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
sudo apt-get install nodejs

Make sure you have successfully installed node.js and NPM on your system

node --version
npm --version

Step 2 – Install Angular/CLI on Debian

After finishing the Node.js installation on your system, use the following commands to install the Angular CLI tool on your system globally.

npm install -g @angular/cli

The above command will install the latest available Angular CLI version on your Debian system. To install specific Angular version run command as following with version number.

npm install -g @angular/cli@6     #Angular 6
npm install -g @angular/cli@7     #Angular 7
npm install -g @angular/cli@8     #Angular 8
npm install -g @angular/cli@9     #Angular 9

Using the -g above command will install the Angular CLI tool globally. So it will be accessible to all users and applications on the system. Angular CLI provides a command ng used for command-line operations. Let’s check the installed version of ng on your system.

ng --version


    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 8.1.3
Node: 12.7.0
OS: linux x64
Angular:
...

Package                      Version
------------------------------------------------------
@angular-devkit/architect    0.801.3
@angular-devkit/core         8.1.3
@angular-devkit/schematics   8.1.3
@schematics/angular          8.1.3
@schematics/update           0.801.3
rxjs                         6.4.0

Step 3 – Create New Angular Application

Now, create a new application named hello-angular4 using the Angular CLI tools. Execute the commands to do this:

ng new hello-angular4

Output:

...
...
added 1011 packages from 1041 contributors and audited 19005 packages in 55.774s
found 0 vulnerabilities

    Successfully initialized git.

This will create a directory named hello-angular4 in your current directory, and create an application.

Step 4 – Serve Angular Application

Your basic Angular application is ready to serve. Change directory to hello-angular4 and run your Angular application using ng serve command.

cd hello-angular4
ng serve

You can access your angular application on localhost port 4200, Which is the default host and port used by Angular application.

• http://localhost:4200

You can change host and port for running Angular application by providing –host and –port command line arguments.

ng serve --host 0.0.0.0 --port 8080

The IP address 0.0.0.0 listens on all interfaces and publically accessible.

Conclusion

You have successfully installed Angular CLI and created a sample application. The next tutorial will help you to configure the Angular application behind the Apache server to serve with a domain name.

The post How to Install Angular CLI on Debian 10/9/8 appeared first on TecAdmin.

Reference: Serve Node.js Application behind the Apache Server

Step 1 – Install Node.js

First of all, you need to install node.js on your system. If you don’t have node.js installed use the following set of commands to add node.js PPA in your Ubuntu system and install it.

sudo apt install python-software-properties
curl -sL https://deb.nodesource.com/setup_14.x | sudo -E bash -
sudo apt install nodejs

Make sure you have successfully installed node.js and NPM on your system

node --version
npm --version

Step 2 – Install Angular/CLI

After installation of node.js and npm on your system, use following commands to install Angular cli tool on your system.

npm install -g @angular/cli

The latest version of Angular CLI will be installed on your Ubuntu Linux system. You may require older Angular version on your machine. To install specific Angular version run command as following with version number.

npm install -g @angular/cli@10        #Angular 10
npm install -g @angular/cli@11        #Angular 11
npm install -g @angular/cli@12        #Angular 12

Using the -g above command will install the Angular CLI tool globally. So it will be accessible to all users and applications on the system. Angular CLI provides a command ng used for command-line operations. Let’s check the installed version of ng on your system.

ng --version


     _                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 12.2.11
Node: 14.15.3
Package Manager: npm 6.14.9
OS: linux x64

Angular: undefined
...

Package                      Version
------------------------------------------------------
@angular-devkit/architect    0.1202.11 (cli-only)
@angular-devkit/core         12.2.11 (cli-only)
@angular-devkit/schematics   12.2.11 (cli-only)
@schematics/angular          12.2.11 (cli-only)

Step 3 – Create a New Angular Application

Now, create a new application named hello-angular4 using the Angular CLI tools. Execute the commands to do this:

ng new hello-angular

Output:

...
...
 Packages installed successfully.
    Successfully initialized git.

This will create a directory named hello-angular in your current directory, and create an application.

Step 4 – Serve Angular Application

Your basic Angular application is ready to serve. Change directory to hello-angular4 and run your Angular application using ng serve command.

cd hello-angular
ng serve

You can access your angular application on localhost port 4200, Which is the default host and port used by Angular application.

• http://localhost:4200

You can change the host and port for running the Angular applications by providing --host and --port command line arguments.

ng serve --host 0.0.0.0 --port 8080

The IP address 0.0.0.0 listens on all interfaces and is publically accessible.

Conclusion

You have successfully installed Angular CLI and created a sample application. The next tutorial will help you to configure the Angular application behind the Apache server to serve with a domain name.

The post How to Install Angular CLI on Ubuntu 18.04 & 16.04 appeared first on TecAdmin.

Empty Array in JavaScript

Use the following syntax to empty an Array. Here myArray is the name of Array.

myArray = [];

The above code will create an Array named myArray with no content. If the myArray already exists, will lose all the existing elements.

You can also set the length to 0 to make it empty.

myArray.length = 0

The post How to Empty an Array in JavaScript appeared first on TecAdmin.

Time is an important part of our life and we cannot avoid it. In our daily routine, we need to know the current date or time frequently. JavaScript provides a global variable Date which helps you to get the current Date & Time in JavaScript. However, it won’t give you accurate information and rather return the local computer time instead of UTC time. To get accurate Date & Time in JavaScript, you need to use different APIs provided by JavaScript itself. You can also get the date and time in your formats like YYYY-MM-DD and HH:MM:SS formats.

This article explains all about getting the current Date & Time in JavaScript with examples and best practices.

Get Current Date & Time in JavaScript

Use the Date() function to create an object in JavaScript with the current date and time. This provides output in the UTC timezone.

var today = new Date();

1. Current Date in JavaScript

Use the following script to get the current date using JavaScript in “Y-m-d” format.

var today = new Date();
var date = today.getFullYear()+'-'+(today.getMonth()+1)+'-'+today.getDate();

• getFullYear() – Provides current year like 2022.
• getMonth() – Provides current month values 0-11. Where 0 for Jan and 11 for Dec. So added +1 to get the result.
• getDate() – Provides day of the month values 1-31.

2. Current Time in JavaScript

Use the following script to get the current time using JavaScript in “H:i:s” format.

var today = new Date();
var time = today.getHours() + ":" + today.getMinutes() + ":" + today.getSeconds();

• getHours() – Provides current hour between 0-23.
• getMinutes() – Provides current minutes between 0-59.
• getSeconds() – Provides current seconds between 0-59.

3. Current Date & Time Both in JavaScript

Use the following script to get the current date and time using JavaScript in the “Y-m-d H:i:s” format. You can simply combine the output of the above JavaScript code in one variable as below:

var today = new Date();
var date = today.getFullYear()+'-'+(today.getMonth()+1)+'-'+today.getDate();
var time = today.getHours() + ":" + today.getMinutes() + ":" + today.getSeconds();
var dateTime = date+' '+time;

console.log(dateTime)

Output
2022-8-4 11:0:38

The post How to Get Current Date & Time in JavaScript appeared first on TecAdmin.

This tutorial describes 2 methods to remove the last character from a string in JavaScript programming language. You can use any one of the following methods as per the requirements.

Method 1 – Using substring() function

Use the substring() function to remove the last character from a string in JavaScript. This function returns the part of the string between the start and end indexes, or to the end of the string.

Syntax:

str.substring(0, str.length - 1);

Example:

// Initialize variable with string
var str = "Hello TecAdmin!";

// Remove last character of string
str = str.substring(0, str.length - 1);

// Print result string
console.log(str)

Method 2 – Using slice() function

Use the slice() function to remove the last character from any string in JavaScript. This function extracts a part of any string and return as new string. When you can store in a variable.

Syntax:

str.slice(0, -1);

Example:

// Initialize variable with string
var str = "Hello TecAdmin!";

// Remove last character of string
str = str.slice(0, -1);

// Print result string
console.log(str)

Wrap Up

In this tutorial, you have learned about removing the last character of a sting in JavaScript. We used substring() and slice() functions to alter a string.

The post 2 Methods to Remove Last Character from String in JavaScript appeared first on TecAdmin.

Syntax:

The syntax of JavaScript every() method is as below.

array.every(function(currentValue, index, arr), thisValue)

JavaScript every() Method Example:

In below example, first we initialize an array named heights with some numeric elements. Now use every() method to find if any array element is greater than 25. The function checkHeight() with exit with array element with value 33.

<script type="text/javascript">
var heights = [15, 24, 33, 12];

function checkHeight(a) {
    return a >= 25;
}

var result = heights.every(checkHeight);
console.log(result);
</script>

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