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Undeclared vs Undefined in JavaScript
Undeclared − It occurs when a variable which hasn’t been declared using var, let or const is being tried to access.
Undefined − It occurs when a variable has been declared using var, let or const but isn’t given a value.
Following is the code for undeclared and undefined in JavaScript −
Example
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
body {
font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
}
.result {
font-size: 18px;
font-weight: 500;
color: blueviolet;
}
</style>
</head>
<body>
<h1>Undeclared vs Undefined</h1>
<div class="result"></div>
<div class="result"></div>
<button class="Btn">Click here</button>
<h3>Click on the above button to access undeclared and undefined variable</h3>
<script>
let BtnEle = document.querySelector(".Btn");
let resEle = document.querySelectorAll(".result");
let a;
BtnEle.addEventListener("click", () => {
resEle[0].innerHTML += "Accessing undefined variable = " + a;
try {
resEle[1].innerHTML = b;
} catch (err) {
resEle[1].innerHTML = "Accessing undeclared variable = " + err;
}
});
</script>
</body>
</html>
Output
On clicking the ‘CLICK HERE’ button −
Updated on: 2020-07-16T13:52:48+05:30
1K+ Views
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