Detailed explanation of js floating point calculation problems

Analysis

JavaScript has only one number type Number, and all numbers in Javascript are expressed in the IEEE-754 standard format. The precision problem of floating point numbers is not unique to JavaScript, because some decimals have infinite digits when expressed in binary:

0.1              0.0001100110011001100110011001100110011001100110011001101
0.2              0.001100110011001100110011001100110011001100110011001101
0.3              0.010011001100110011001100110011001100110011001100110011
0.5              0.1
0.6              0.10011001100110011001100110011001100110011001100110011

So for example 1.1, the program actually cannot It really represents '1.1', but it can only be accurate to a certain extent. This is an inevitable loss of precision:

1.09999999999999999

In JavaScript, the problem is more complicated, here is just Give some test data in Chrome:

 输入               输出1.0-0.9 == 0.1     False1.0-0.8 == 0.2     False1.0-0.7 == 0.3     False1.0-0.6 == 0.4     True1.0-0.5 == 0.5     True1.0-0.4 == 0.6     True1.0-0.3 == 0.7     True1.0-0.2 == 0.8     True1.0-0.1 == 0.9     True

Solution

So how to avoid this type of ` 1.0-0.9 != 0.1 ` non-bug type problems? The following is a commonly used solution. The calculation result is reduced in precision before judging the floating point operation result, because the precision reduction process will always be automatically rounded:

(1.0-0.9).toFixed(digits)     // toFixed() 精度参数须在 0 与20 之间(1.0-0.9).toFixed(10)== 0.1   // 结果为True(1.0-0.8).toFixed(10)== 0.2   // 结果为True(1.0-0.7).toFixed(10)== 0.3   // 结果为True(11.0-11.8).toFixed(10) == -0.8   // 结果为TrueparseFloat((1.0-0.9).toFixed(10)) === 0.1   // 结果为TrueparseFloat((1.0-0.8).toFixed(10)) === 0.2   // 结果为TrueparseFloat((1.0-0.7).toFixed(10)) === 0.3   // 结果为TrueparseFloat((11.0-11.8).toFixed(10)) === -0.8   // 结果为True

Method refining

// 通过isEqual工具方法判断数值是否相等function isEqual(number1, number2, digits){
    digits = digits || 10; // 默认精度为10return number1.toFixed(digits) === number2.toFixed(digits);
}

isEqual(1.0-0.7, 0.3);  // return true// 原生扩展方式，更喜欢面向对象的风格Number.prototype.isEqual = function(number, digits){
    digits = digits || 10; // 默认精度为10return this.toFixed(digits) === number.toFixed(digits);
}

(1.0-0.7).isEqual(0.3); // return true

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