Number() vs parseInt()
Written byPhuoc Nguyen
Category
JavaScript
Created
10 Jun, 2020
Last updated
21 Dec, 2022
Both
`Number()`
and `parseInt()`
are often used to convert a string to number.#Differences
-
`Number()`
converts the type whereas parseInt parses the value of input.// ParsingparseInt('32px'); // 32parseInt('5e1'); // 5// Convert typeNumber('32px'); // NaNNumber('5e1'); // 50As you see,`parseInt`
will parse up to the first non-digit character. On the other hand,`Number`
will try to convert the entire string. -
`parseInt`
accepts two parameters. The second parameter is used to indicate the radix number.parseInt('0101'); // 101parseInt('0101', 10); // 101parseInt('0101', 2); // 5Number('0101'); // 101 -
They return different results when we passing special values such as
`undefined`
or`null`
:parseInt(); // NaNparseInt(null); // NaNparseInt(true); // NaNparseInt(''); // NaNNumber(); // 0Number(null); // 0Number(true); // 1Number(''); // 0
#Good practices
-
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'); // 15parseInt('0XF'); // 15parseInt('0xF', 16); // 15parseInt('0xF', 10); // 0Since the method could be implemented differently in different versions of JavaScript and browsers, it's recommended to pass the radix number. -
-
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 '); // 5parseInt('12 345'); // 12, not 12345To avoid the similar situations, you should remove all spaces before parsing:parseInt(value.replace(/\s+/g, ''), 10); -
Don't use
`new Number()`
to compare the numbers.Number('2') == 2; // trueNumber('2') === 2; // truenew Number('2') == 2; // truenew Number('2') === 2; // falseconst a = new Number('2');const b = new Number('2');a == b; // falsea === b; // false
#Tip
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
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Phước Nguyễn