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# Number() vs parseInt()

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

## #Differences

1. ``Number()`` converts the type whereas parseInt parses the value of input.
js
``// ParsingparseInt('32px'); // 32parseInt('5e1'); // 5// Convert typeNumber('32px'); // NaNNumber('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.
js
``parseInt('0101'); // 101parseInt('0101', 10); // 101parseInt('0101', 2); // 5Number('0101'); // 101``
3. They return different results when we passing special values such as ``undefined`` or ``null``:
js
``parseInt(); // NaNparseInt(null); // NaNparseInt(true); // NaNparseInt(''); // NaNNumber(); // 0Number(null); // 0Number(true); // 1Number(''); // 0``

## #Good practices

1. Always pass the radix to ``parseInt``.
The ``parseInt`` method takes two parameters:
js
``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).
js
``parseInt('0xF'); // 15parseInt('0XF'); // 15parseInt('0xF', 16); // 15parseInt('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:
js
``parseInt('   5   '); // 5parseInt('12 345'); // 12, not 12345``
To avoid the similar situations, you should remove all spaces before parsing:
js
``parseInt(value.replace(/\s+/g, ''), 10);``
3. Don't use ``new Number()`` to compare the numbers.
js
``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:
js
``+'010'; // 10+'2e1'; // 20+'0xF'; // 15``

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Phước Nguyễn