What is Undefined in JavaScript ?
Last Updated :
07 Feb, 2024
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In JavaScript, undefined is a primitive value that is automatically assigned to variables that have been declared but not yet initialized with a value. It's also the default return value of functions that do not explicitly return anything.
Here are some key points about undefined:
- It represents the absence of a value.
- It's a primitive data type.
- It's automatically assigned to variables that have been declared but not yet assigned a value.
- It's returned when accessing properties of an object that do not exist.
- It's considered a falsy value, meaning it evaluates to
falsein a Boolean context.
Example: Here, the variable x is declared but not assigned a value, so it automatically gets the value undefined. In the second example, the function greet() is called without passing any arguments, so the parameter name inside the function has the value undefined.
let x;
console.log(x); // Output: undefined
function greet(name) {
console.log(`Hello, ${name}!`);
}
greet(); // Output: Hello, undefined!
Output
undefined Hello, undefined!
