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How is JavaScript an untyped language?
JavaScript is an untyped (or dynamically typed) language because variables can hold any data type without explicit type declaration. Unlike statically typed languages like Java, C#, C++ that require type declarations like int, char, float, JavaScript uses var, let, and const to create variables of any type.
One of the key advantages of untyped languages is the flexibility to reassign different data types to the same variable during runtime.
Dynamic Type Assignment
In this example, we create a variable named "x" and assign different data types to it. At each step, we print the type of the variable using typeof.
<html>
<head>
<title>Example - JavaScript is an untyped language</title>
</head>
<body>
<h2>JavaScript is an untyped language</h2>
<p>Printing the type of variable after reassigning multiple data types into it.</p>
<p id="result"></p>
</body>
<script>
let x = 10;
document.getElementById("result").innerHTML += typeof x + "<br>";
x = "Tutorials Point";
document.getElementById("result").innerHTML += typeof x + "<br>";
x = [1, 2, 3, 4, 5, 6];
document.getElementById("result").innerHTML += typeof x + "<br>";
x = {name: "Saurabh"};
document.getElementById("result").innerHTML += typeof x + "<br>";
x = undefined;
document.getElementById("result").innerHTML += typeof x + "<br>";
x = null;
document.getElementById("result").innerHTML += typeof x + "<br>";
x = function(){};
document.getElementById("result").innerHTML += typeof x + "<br>";
</script>
</body>
</html>
number string object object undefined object function
Type Coercion
JavaScript performs automatic type conversion when operating on different data types. For example, adding a number and a string results in string concatenation.
<!DOCTYPE html>
<html>
<head>
<title>How is JavaScript an untyped language</title>
</head>
<body>
<h2>How is JavaScript an untyped language?</h2>
<p>Adding two different type variables.</p>
<p id="result"></p>
</body>
<script>
let x = 2; // Number
let y = "3"; // String
let sum = x + y;
document.getElementById("result").innerHTML += sum + "<br>"; // 23
document.getElementById("result").innerHTML += typeof sum; // String
</script>
</body>
</html>
23 string
Variable Declaration Keywords
In this example, we define three variables using different declaration keywords: var, let, and const.
<html>
<body>
<p id="result"></p>
<script>
var age1 = 20;
let age2 = 18;
const age3 = 32;
function check(age){
if (age > 18) {
document.getElementById("result").innerHTML += "Qualified for driving<br>";
} else {
document.getElementById("result").innerHTML += "Not Qualified for driving<br>";
}
}
check(age1);
check(age2);
check(age3);
</script>
</body>
</html>
Qualified for driving Not Qualified for driving Qualified for driving
String and Boolean Concatenation
This example demonstrates how JavaScript automatically converts a boolean to a string when concatenating with a string.
<html>
<head>
</head>
<body>
<script>
const price = "Is price good?";
var flag = true;
document.write(price + flag);
</script>
</body>
</html>
Is price good?true
Conclusion
JavaScript's untyped nature provides flexibility in variable assignment and automatic type conversion. This makes JavaScript easier to write but requires careful attention to avoid unexpected type coercion behaviors.
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