← Errors
NaN (Not a Number) is a special IEEE 754 value that propagates silently through calculations. Once a NaN enters a computation, every subsequent result is also NaN. It is produced by invalid numeric operations like parsing non-numeric strings or dividing zero by zero.
Why it happens
- •Calling parseInt() or parseFloat() on a string that does not begin with a number.
- •Performing arithmetic on undefined (undefined + 1 === NaN).
- •Using Math functions with non-numeric input (Math.sqrt(-1)).
- •An array reduction with no initial value on an empty array.
Examples
JavaScript
Code that triggers the error
const price = parseFloat("$19.99");
const tax = price * 0.2;
console.log(tax); // NaNError output
NaN
How to fix it
Validate numeric input before arithmetic. Use Number.isNaN() (not the global isNaN()) to check for NaN since isNaN('') returns true. Always provide an initial value to Array.reduce(). Strip currency symbols and formatting before parsing money values.
Fixed code
const raw = "$19.99";
const price = parseFloat(raw.replace(/[^0-9.]/g, ""));
if (isNaN(price)) throw new Error(`Cannot parse price: ${raw}`);
const tax = price * 0.2;
console.log(tax); // 3.998Related errors
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