JavaScript: isNaN() function


The isNaN function is used to determine whether a value is "NaN" (not a number) or not. isNaN is a top-level function and is not associated with any object.




testvalue: The value to evaluate.

Example: isNaN() function

The following example shows how to use isNaN() function.

JavaScript Code:

console.log(isNaN("Good Morning"));

View the example in the browser

Live demo:

See the Pen isnan-function-1 by w3resource (@w3resource) on CodePen.

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JavaScript: Tips of the Day

JavaScript: semicolon (;)

function nums(a, b) {
  if (a > b) console.log('a is bigger');
  else console.log('b is bigger');
  a + b;

console.log(nums(4, 2));
console.log(nums(1, 2));

In JavaScript, we don't have to write the semicolon (;) explicitly, however the JavaScript engine still adds them after statements. This is called Automatic Semicolon Insertion. A statement can for example be variables, or keywords like throw, return, break, etc.
Here, we wrote a return statement, and another value a + b on a new line. However, since it's a new line, the engine doesn't know that it's actually the value that we wanted to return. Instead, it automatically added a semicolon after return. You could see this as:

a + b;
This means that a + b is never reached, since a function stops running after the return keyword. If no value gets returned, like here, the function returns undefined. Note that there is no automatic insertion after if/else statements!

Ref: https://bit.ly/3jFRBje