How to declare variables in JavaScript?

In JavaScript, variables are used to store data values. These values can be of different data types, such as numbers, strings, or boolean values. To declare a variable, you use the keyword "var" followed by the variable name like this:

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var myVariable;
You can also assign a value to the variable at the time of declaration like this:

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var myVariable = "Hello World";
Once you have declared a variable, you can change its value by assigning a new value to it, like this:

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myVariable = "Goodbye World";
You can also declare and assign values to multiple variables at once, like this:

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var firstName = "John", lastName = "Doe", age = 25;
JavaScript also has two other keywords you can use to declare variables: "let" and "const". The "let" keyword declares a block-scoped variable that can be reassigned, while the "const" keyword declares a block-scoped variable that cannot be reassigned.

Here's an example of how to use "let" and "const" variables:

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let myLetVariable = "Hello World";
myLetVariable = "Goodbye World"; // OK, can be reassigned

const myConstVariable = "Hello World";
myConstVariable = "Goodbye World"; // ERROR, cannot be reassigned