Javascript Variables

To declare a Variable in JavaScript, you can use the var, let, or const keywords, followed by the variable name. Here's an example:

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var age;
let name;
const PI = 3.14;

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JavaScript is a dynamically typed language, which means you don't have to explicitly specify the data type of a variable. It is determined automatically based on the value assigned to it. For example:

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var message = "Hello"; // string
var count = 10; // number
var isTrue = true; // boolean

You can assign values to Variables using the assignment operator (=). Here's an example :

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var age = 25;
var name = "John";

Once a Variable is declared and assigned a value, you can update its value by assigning a new value to it. Here's an example :

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var count = 5;
count = count + 1; // updated value: 6

In the example above, the variable count is initially assigned the value of 5. The next line of code updates the value of count by adding 1 to its current value. The comment "// updated value: 6" explains that the new value of count after the update operation is 6.

JavaScript has both global and local variable scopes. Variables declared outside any function have a global scope, while variables declared within a function have a local scope.
Variable hoisting is a JavaScript behavior where variables declared with var are moved to the top of their scope. Here's an example :

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console.log(age); // Output: undefined
var age = 30;

• In the example above, the code attempts to log the value of the age variable using console.log(). However, before the variable age is declared and assigned a value, the console.log(age) line is encountered. At this point, the variable age is in a state called "hoisting," where it exists but doesn't have a defined value yet. As a result, the output of the console.log(age) statement will be undefined.
• The comment "// Output: undefined" is added to clarify that running that line of code will produce the value undefined in the console.

In JavaScript, You can declare constants using the const keyword. Constants are variables that cannot be reassigned. when you declare a variable using the const keyword, it creates a constant variable whose value cannot be changed or reassigned. If you try to assign a new value to a constant variable, you will encounter a runtime error, and the JavaScript engine will throw an error similar to "// Error: Assignment to a constant variable".
Here's an example:

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const PI = 3.14;
PI = 3.14159; // Error: Assignment to a constant variable

In the example above, attempting to assign a new value to the PI constant will result in an error because constants are meant to be immutable and cannot be changed after declaration.

Remember to use meaningful variable names, follow naming conventions, and be consistent in your code. Understanding variables is fundamental to JavaScript programming, as they allow you to store and manipulate data throughout your code.