Converting to numbers

Learn to convert strings to numbers with parseInt, parseFloat and Number().

parseInt: String to integer

parseInt reads the integer at the start of a string. It walks until a non digit character and ignores the rest.

The second argument is the radix (base) that tells which number system to read in. Always pass 10 for the decimal system:

const quantity = parseInt("3 pens", 10);
// quantity = 3

If you skip the radix JavaScript may read some strings as octal (base 8); always writing 10 explicitly is safer.

parseFloat reads from the start of a string just like parseInt, but it also accepts a decimal dot. It stops at a non number character.

Number is stricter: the whole string must be a valid number. If there is junk at either end it returns NaN.

For example:

Assign parseInt("3", 10) to quantity and parseFloat("19.99") to price (both as const). Then log both with console.log.

Show example solution

const quantity = parseInt("3", 10);
const price = parseFloat("19.99");
console.log(quantity);
console.log(price);

Parse a hexadecimal value

const hex = parseInt("ff", ____);

Show answer

const hex = parseInt("ff", 16);