Why Javascript Numbers Are Weird
(And How to Fix It)
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We use
a decimal system.
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0
12
345
6789
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345
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345
5
40
300
+
+
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345
5
5 x 1
40
4 x 10
+
+
300
3 x 100
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345
5
5 x 1
5 x 10^0
40
4 x 10
4 x 10^1
+
+
300
3 x 100
3 x 10^2
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Computers use a binary system.
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Computers must convert decimal to binary.
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5
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5
1 x 2^2 (4)
5 - 4 = 1
1
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5
0 x 2^1 (2)
1 - 0 = 1
10
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5
1 x 2^0 (1)
1 - 1 = 0
101
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101
1
0
4
+
+
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Double-precision
floating-point format
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System.out.println(.1 + .2);
// 0.30000000000000004print(.1 + .2)
# 0.30000000000000004Python
Java
puts 0.1 + 0.2
# 0.30000000000000004Ruby
Console.WriteLine("{0:R}", .1 + .2);
// 0.30000000000000004C#
console.log(.1 + .2);
// 0.30000000000000004JavaScript
Before ES2020
JavaScript only had
the number type
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5
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0.75
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0.75
0.75 x 2 = 1.5
1
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0.75
0.5 x 2 = 1
11
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0.75
O.11
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5.75
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console.log(.1 + .2);
// 0.30000000000000004@frontstuff_io
0.1
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0.1 + 0.2
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Same goes with
Large integers
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Number.MAX_SAFE_INTEGER;
// 9007199254740991
Number.MAX_SAFE_INTEGER + 2;
// 9007199254740992@frontstuff_io
9007199254740991
-9007199254740991
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What to do instead?
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(1 + 2) / 10^1
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Dinero({ amount: 500, currency: "USD" });
// represents $5@frontstuff_io
10n
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9007199254740991n + 2n;
// 9007199254740993n@frontstuff_io
Arbitrary precision math is slower than floating point math.
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Arbitrary precision integers
are still new.
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Thank you!
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