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What does parseInt do?

Learning parseInt with fun examples 🎉

Karthick V

Karthick V

Oct 8, 2022 — Updated Dec 8, 2022 · 2 min read

  1. parseInt() method parses a string to an integer based on a specified radix number in 2nd argument.
  2. It only parses the very first string, any white spaces in between will be considered the end of the parsing.
  3. The return type is an Integer where the decimals are ignored.
  4. The second argument (optional) is based on the radix number system

A radix parameter specifies the number system to use mainly of four systems

  • Binary system specified as 2
  • Octal number system specified as 8
  • Decimal number system specified as 10
  • Hexadecimal number system specified as 16

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const number = "5";
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console.log(number + 5); // "55"
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parseInt(number + 5); // 55
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// parsing defaults to Decimal(10)
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const number = "5.5";
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console.log(number + 5); // "5.55"
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parseInt(number + 5); // 10
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// The decimal will be ignored
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const input = "53abc";
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console.log(number + 5); // "53abc5"
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parseInt(number) + 5; // 58
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// The value "abc" is not a number and js will ignore them
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// Tricky one 🎃
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parseInt("-0XF"); // -15
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// parsing defaults to hexadecimal since begins with `0x`


_16
const input = "5 3abc";
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console.log(number + 5); // "5 3abc5"
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parseInt(number + 5); // 10
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// Because the white space after 5 will be considered the end
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parseInt("100", 2); // 4
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// Takes binary number system.
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parseInt("100", 8); // 64
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// Considers octal number system.
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parseInt("100", 10); // 100
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// Which is the decimal number system and the default radix parameter as well
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parseInt("100", 16); // 256
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// 16 belongs to the hexadecimal number system.

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