Undefined type in JavaScript

Below is the JavaScript code snippet I have written.

function bar() {

var x = "Amy";
x = parseInt(x);
console.log(x);
if (isNaN(x)) {
    console.log("Your entry is not a number");
} else {
    if (typeof (x) === "number") {
        console.log("number");
    } else if (typeof (x) === "string") {
        console.log("string");
    }
}

}

When trying to parse an integer from a string, NaN was returned as the value.

It is known that typeof(NaN) returns "number" and numbers can be compared directly in an IF condition. However, this approach did not work in this case.

After attempting isNaN(x), it successfully identified when x was not a number, while x!=NaN failed to do so.

Why is this? Any insights?

Answer №1

The importance of having an isNaN function

When working with JavaScript, it becomes evident that determining if a value is NaN or not cannot be done using the equality operators (== and ===). This is because both NaN == NaN and NaN === NaN return false. Therefore, having an isNaN function is essential.[Source]

In summary: NaN does not equate to anything, even itself, so it's necessary to use the Number.isNaN(value) method for accurate results.

console.log(NaN == NaN);
console.log(NaN === NaN);
console.log(NaN === undefined);
console.log(NaN === null);
console.log(NaN === 'TEST');
console.log(NaN === 0);

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