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In JavaScript, var is one of the three ways to declare variables, along with let and const. Here's a detailed overview of how var works and its characteristics:

Characteristics of `var`:

1) Function Scope:

Variables declared with var are function-scoped. This means they are only accessible within the function in which they are defined. However, if declared outside a function, they become global variables.

Example

<!DOCTYPE html>

<html>

<head>

<title>Online HTML Editor</title>

</head>

<body>

function test() {

var x = 10;

console.log(x); // Outputs: 10

}

test();

console.log(x);// Error: x is not defined (x is function-scoped)

</script>

</body>

</html>

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2) Re-declaration:

You can re-declare variables using var within the same scope without any errors.

Example

<!DOCTYPE html>

<html>

<head>

<title>Online HTML Editor</title>

</head>

<body>

var name = "Alice";

var name = "Bob"; // No error, but overwrites the previous value

console.log(name); // Outputs: Bob

</script>

</body>

</html>

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3) Global Variables:

When a var is declared outside any function, it becomes a property of the global object.

Example

<!DOCTYPE html>

<html>

<head>

<title>Online HTML Editor</title>

</head>

<body>

var globalVar = "I am global";

console.log(window.globalVar); // Outputs: "I am global"

</script>

</body>

</html>

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4) No Block Scope:

var does not respect block scope (i.e., { ... } created by loops or conditionals). This means that variables declared with var are accessible outside of blocks, even if they are declared inside.

Example

<!DOCTYPE html>

<html>

<head>

<title>Online HTML Editor</title>

</head>

<body>

if (true) {

var num = 10;

}

console.log(num); // Outputs: 10 (even though num is inside the block)

</script>

</body>

</html>

Try it yourself

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Characteristics of var:

Characteristics of `var`: