Does parseDouble exist in JavaScript?

javascript floating-point-precision
Priyesh Shah picture Priyesh Shah · Jan 22, 2014 · Viewed 63.4k times · Source

In JavaScript, I have a number which is 21 digits, and I want to parse it.

Does a parseDouble method exist in JavaScript?

Answer

user2864740 picture user2864740 · Jan 22, 2014

It's not possible to natively deal with a 21-digit precision number in JavaScript.

JavaScript only has one kind of number: "number", which is a IEEE-754 Double Precision ("double") value. As such, parseFloat in JavaScript is the equivalent of a "parse double" in other languages.

However, a number/"double" only provides 16 significant digits (decimal) of precision and so reading in a number with 21-digits will lose the 5 least significant digits1.

For more precision (or accuracy) a "big number" library must be used;

1 Information can be lost when encoding as an IEEE "double", which cannot encode all decimal values exactly, but that's another question..

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