← Back tothis vs that

Number() vs parseInt()

Written byPhuoc Nguyen
10 Jun, 2020
Last updated
21 Dec, 2022
Both `Number()` and `parseInt()` are often used to convert a string to number.


  1. `Number()` converts the type whereas parseInt parses the value of input.
    // Parsing
    parseInt('32px'); // 32
    parseInt('5e1'); // 5

    // Convert type
    Number('32px'); // NaN
    Number('5e1'); // 50
    As you see, `parseInt` will parse up to the first non-digit character. On the other hand, `Number` will try to convert the entire string.
  2. `parseInt` accepts two parameters. The second parameter is used to indicate the radix number.
    parseInt('0101'); // 101
    parseInt('0101', 10); // 101
    parseInt('0101', 2); // 5

    Number('0101'); // 101
  3. They return different results when we passing special values such as `undefined` or `null`:
    parseInt(); // NaN
    parseInt(null); // NaN
    parseInt(true); // NaN
    parseInt(''); // NaN

    Number(); // 0
    Number(null); // 0
    Number(true); // 1
    Number(''); // 0

Good practices

  1. Always pass the radix to `parseInt`.
    The `parseInt` method takes two parameters:
    parseInt(value, radix);
    The second parameter specifies the current numeral system. In the case it's not specified, then it will be set automatically based on the value.
    • If the value starts with `0x` or `0X`, then the radix is 16 (hexadecimal)
    • In other cases, the radix is 10 (decimal).
    In the older versions of JavaScript, if the string starts with 0 then the radix is set as 8 (octal).
    parseInt('0xF'); // 15
    parseInt('0XF'); // 15
    parseInt('0xF', 16); // 15

    parseInt('0xF', 10); // 0
    Since the method could be implemented differently in different versions of JavaScript and browsers, it's recommended to pass the radix number.
  2. Trim the spaces before parsing the number.
    Both `Number()` and `parseInt` accept the spaces in input. But be aware that you could get different result when passing a value with spaces as following:
    parseInt(' 5 '); // 5
    parseInt('12 345'); // 12, not 12345
    To avoid the similar situations, you should remove all spaces before parsing:
    parseInt(value.replace(/\s+/g, ''), 10);
  3. Don't use `new Number()` to compare the numbers.
    Number('2') == 2; // true
    Number('2') === 2; // true

    new Number('2') == 2; // true
    new Number('2') === 2; // false

    const a = new Number('2');
    const b = new Number('2');

    a == b; // false
    a === b; // false


Instead of using the `Number()` constructor to convert a string to number, you can use the `+` operator:
+'010'; // 10
+'2e1'; // 20
+'0xF'; // 15

See also

Questions? 🙋

Do you have any questions? Not just about this specific post, but about any topic in front-end development that you'd like to learn more about? If so, feel free to send me a message on Twitter or send me an email. You can find them at the bottom of this page.
I have a long list of upcoming posts, but your questions or ideas for the next one will be my top priority. Let's learn together! Sharing knowledge is the best way to grow 🥷.

Recent posts ⚡

Newsletter 🔔

If you're into front-end technologies and you want to see more of the content I'm creating, then you might want to consider subscribing to my newsletter.
By subscribing, you'll be the first to know about new articles, products, and exclusive promotions.
Don't worry, I won't spam you. And if you ever change your mind, you can unsubscribe at any time.
Phước Nguyễn