BigNumber 讲解

安装

Browser:

<script src='path/to/bignumber.js'></script>

Node.js:

$ npm install --save bignumber.js

var BigNumber = require('bignumber.js');

ES6 module (bignumber.mjs):

//import BigNumber from 'bignumber.js';
import {BigNumber} from 'bignumber.js';

AMD loader libraries such as requireJS:

require(['bignumber'], function(BigNumber) {
    // Use BigNumber here in local scope. No global BigNumber.
});

使用

示例一：
bignumber.js 库中提供一个 BigNumber 的构造函数，参数必须是长度在15位以内的数字

x = new BigNumber(123.4567)
y = BigNumber('123456.7e-3')
z = new BigNumber(x)
x.isEqualTo(y) && y.isEqualTo(z) && x.isEqualTo(z)      // true

示例二：
可以使用2-36进制的数，超过36进制的也可以，不过需要自定义字母来表示了。0-9 加上a-z刚好到36，所以超过36就无法表示了，需要你定义其他的符号来表示了。

x = new BigNumber(1011, 2)          // "11"
y = new BigNumber('zz.9', 36)       // "1295.25"
z = x.plus(y)                       // "1306.25"

示例三：
做小数运算

0.3 - 0.1                           // 0.19999999999999998
x = new BigNumber(0.3)
x.minus(0.1)                        // "0.2"
x                                   // "0.3"

示例四：
链式语法调用

x.dividedBy(y).plus(z).times(9)
x.times('1.23456780123456789e+9').plus(9876.5432321).dividedBy('4444562598.111772').integerValue()

示例五：
有些方法名比较长的，有别名表示 比如 isEqualTo 和eq

x.squareRoot().dividedBy(y).exponentiatedBy(3).isEqualTo( x.sqrt().div(y).pow(3) )    // true
x.modulo(y).multipliedBy(z).eq( x.mod(y).times(z) )                                   // true

示例六：
和 js的Number类型类似，有一些常用的方法：

x = new BigNumber(255.5)
x.toExponential(5)                  // "2.55500e+2"
x.toFixed(5)                        // "255.50000"
x.toPrecision(5)                    // "255.50"
x.toNumber()                        // 255.5

toString方法

x.toString(16)                     // "ff.8"

There is also a toFormat method which may be useful for internationalisation

y = new BigNumber('1234567.898765')
y.toFormat(2)                       // "1,234,567.90"

The maximum number of decimal places of the result of an operation involving division (i.e. a division, square root, base conversion or negative power operation) is set using the config method of the BigNumber constructor.

The other arithmetic operations always give the exact result.

BigNumber.config({ DECIMAL_PLACES: 10, ROUNDING_MODE: 4 })

x = new BigNumber(2);
y = new BigNumber(3);
z = x.dividedBy(y)                        // "0.6666666667"
z.squareRoot()                            // "0.8164965809"
z.exponentiatedBy(-3)                     // "3.3749999995"
z.toString(2)                             // "0.1010101011"
z.multipliedBy(z)                         // "0.44444444448888888889"
z.multipliedBy(z).decimalPlaces(10)       // "0.4444444445"

There is a toFraction method with an optional maximum denominator argument

y = new BigNumber(355)
pi = y.dividedBy(113)               // "3.1415929204"
pi.toFraction()                     // [ "7853982301", "2500000000" ]
pi.toFraction(1000)                 // [ "355", "113" ]

and isNaN and isFinite methods, as NaN and Infinity are valid BigNumber values.

x = new BigNumber(NaN)                                           // "NaN"
y = new BigNumber(Infinity)                                      // "Infinity"
x.isNaN() && !y.isNaN() && !x.isFinite() && !y.isFinite()        // true

BigNumber的值以系数，指数和符号的形式,以十进制浮点格式进行存储
c 是coefficient 系数
c 是exponent 指数，最高位后有几个零
s 是sign 符号，也就是正负

x = new BigNumber(-123.456);
x.c                                 // [ 123, 45600000000000 ]  coefficient (i.e. significand)
x.e                                 // 2                        exponent
x.s                                 // -1                       sign

For advanced usage, multiple BigNumber constructors can be created, each with their own independent configuration which applies to all BigNumber's created from it.

// Set DECIMAL_PLACES for the original BigNumber constructor
BigNumber.config({ DECIMAL_PLACES: 10 })

// Create another BigNumber constructor, optionally passing in a configuration object
BN = BigNumber.clone({ DECIMAL_PLACES: 5 })

x = new BigNumber(1)
y = new BN(1)

x.div(3)                            // '0.3333333333'
y.div(3)                            // '0.33333'