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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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