what means undefined in javascript

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In JavaScript, “undefined” is a special value that indicates the absence of a value for a particular variable or property. It’s used to represent variables that have been declared but not assigned a value.

Use Cases

“undefined” is often encountered in scenarios such as:

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  • Declaring a variable without assigning a value
  • Accessing a non-existent object property
  • Function parameters not provided

Usage and Example

Here’s an example illustrating the use of “undefined” in JavaScript:

    let x;
    console.log(x); // Output: undefined
    const person = { name: "Alice" };
    console.log(person.age); // Output: undefined
    function greet(name) {
        console.log("Hello, " + name);
    greet(); // Output: Hello, undefined

Avoiding “undefined”

Developers can use techniques like default values and conditional checks to handle cases where “undefined” might cause unexpected behavior.


“undefined” in JavaScript represents the absence of a value and is used to indicate cases where a variable or property hasn’t been assigned a value.

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