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JavaScript: The Good Parts by Douglas Crockford

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Floating Point

Binary floating-point numbers are inept at handling decimal fractions, so 0.1 + 0.2 is not equal to 0.3. This is the most frequently reported bug in JavaScript, and it is an intentional consequence of having adopted the IEEE Standard for Binary Floating-Point Arithmetic (IEEE 754). This standard is well-suited for many applications, but it violates most of the things you learned about numbers in middle school. Fortunately, integer arithmetic in floating point is exact, so decimal representation errors can be avoided by scaling.

For example, dollar values can be converted to whole cents values by multiplying them by 100. The cents then can be accurately added. The sum can be divided by 100 to convert back into dollars. People have a reasonable expectation when they count money that the results will be exact.

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