为什么 JavaScript 在解析的数字末尾添加一个额外的非零数字

Question

When I run, Number(123456789012345.12).toFixed(3) , it is returning "123456789012345.125" as a String. Where is last 5 (in the decimal) coming from? I would have expected it to return "123456789012345.120" . I executed this code on Mac with an Intel processor using Chrome version 68.

Answer 1

Your number is too long (has too many digits), it does not fit into the 64-bit floating point precision of a JavaScript number.

Below is an example of using less digits:

Number(123456789012345.12).toFixed(3):  '123456789012345.125'
Number(12345678901234.12).toFixed(3):    '12345678901234.119'
Number(1234567890123.12).toFixed(3):      '1234567890123.120'
Number(123456789012.12).toFixed(3):        '123456789012.120'
Number(12345678901.12).toFixed(3):          '12345678901.120'

JavaScript numbers are represented by a 64-bit floating point value.

It's not possible to represent the number you show using normal JavaScript numbers. You would need to implement something like bignumber.js .

If using bignumber.js then you can do the same using the following:

let BigNumber = require('bignumber.js');
BigNumber('123456789012345.12').toFixed(3):  '123456789012345.120'
BigNumber('12345678901234.12').toFixed(3):    '12345678901234.120'
BigNumber('1234567890123.12').toFixed(3):      '1234567890123.120'
BigNumber('123456789012.12').toFixed(3):        '123456789012.120'