JavaScript variables - var, let and const

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Instead of using the var keyword when defining variables, use the let and const keywords. This is due to the fact that whereas var is function-scoped, let and const are block-scoped. This indicates that var variables can be accessed from anywhere within the enclosing function, but let and const variables can only be accessed within the block in which they are declared. You may avoid unexpected behaviour and make your code simpler to read and comprehend by using let and const.

 Here is an example:

// Using `var` to declare a variable
var x = 10;
if (x > 5) {
  // `y` is accessible within the if block
  var y = 5;
}
// `y` is also accessible outside of the if block
console.log(y); // 5

// Using `let` to declare a variable
let x = 10;
if (x > 5) {
  // `y` is only accessible within the if block
  let y = 5;
}
// `y` is not accessible outside of the if block
console.log(y); // ReferenceError: y is not defined
 

As you can see, in the second example, the y variable is only accessible inside the if block and cannot be used outside of that block because let was used in place of var. This can make your code more readable and help prevent bugs.

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