JS数字精度丢失的原因及解决方案

大纲

1.了解原因
2.解决方案

1.原因

因为在计算机中，数字先转二进制，然后运算，最后转十进制

例如：0.1 + 0.2

0.1 也就是0.0001100110011001100110011001100110011001100110011001101
0.2 也就是0.001100110011001100110011001100110011001100110011001101

即：
0.00011001100110011001100110011001100110011001100110011010 +
0.0011001100110011001100110011001100110011001100110011010 =
0.0100110011001100110011001100110011001100110011001100111

结果0.0100110011001100110011001100110011001100110011001100111再转换成十进制就是0.30000000000000004。

2.解决办法

（1）插件Decimal

0.1 + 0.2                                // 0.30000000000000004
x = new Decimal(0.1)
y = x.plus(0.2)                          // '0.3'

（2）插件bignumber

x = new BigNumber(0.1)
y = x.plus(0.2)

（3）变成整数

function add(num1, num2) {
  const num1Len = (num1.toString().split('.')[1] ).length;
  const num2Len = (num2.toString().split('.')[1] ).length;
  const maxLen = Math.pow(10, Math.max(num1Len, num2Len));
  return (num1 * maxLen + num2 * maxLen) / maxLen;
}