undefined

In JavaScript, a value is considered undefined if it has not been assigned a value or if it has been explicitly set to undefined. There are several ways to check if a value is undefined in JavaScript:

• typeof operator: The typeof operator returns a string indicating the type of the operand. If the operand is undefined, typeof will return “undefined”.
• === operator: The === operator tests for strict equality. If the operand is undefined, === will return false for any other value, including null.
• void operator: The void operator returns undefined. It can be used to explicitly set a variable to undefined.

Checking for undefined values is important in JavaScript because it allows you to handle cases where a value has not been assigned or has been explicitly set to undefined. This can help prevent errors and ensure that your code runs as expected.

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In JavaScript, `undefined` is a primitive value that represents the absence of a value. It is often used to initialize variables before they are assigned a value, or to represent the return value of a function that does not return a value. There are several ways to check if a variable is `undefined` in JavaScript. One way is to use the `typeof` operator. The `typeof` operator returns a string indicating the type of a variable. If the variable is `undefined`, the `typeof` operator will return the string `”undefined”`. For example:

    let x;    console.log(typeof x); // "undefined"  

Another way to check if a variable is `undefined` is to use the `===` operator. The `===` operator compares two values for strict equality. If the two values are `undefined`, the `===` operator will return `true`. For example:

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