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JavaScript: isNaN() function

Description

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.

Syntax

isNan(testvalue)

Parameters

testvalue: The value to evaluate.

Example: isNaN() function

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

JavaScript Code:

console.log(isNaN("Good Morning"));
console.log(isNaN("2009/01/01"));
console.log(isNaN(455));
console.log(isNaN(-9.34));
console.log(isNaN(15-12));
console.log(isNaN(0));

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

Returns the average of an array, after mapping each element to a value using the provided function

Example:

const averageBy = (arr, fn) =>
  arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0) /
  arr.length;

console.log(averageBy([{ n: 2 }, { n: 4 }, { n: 6 }, { n: 8 }], o => o.n)); 
console.log(averageBy([{ n: 1 }, { n: 3 }, { n: 5 }, { n: 7 }], 'n'));

Output:

5
4