JS四则运算，处理精度问题

使用自定义方法

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export const toNonExponential = (num) => {
	if (num == null) {
		return num;
	}
	if (typeof num == "number") {
		var m = num.toExponential().match(/\d(?:\.(\d*))?e([+-]\d+)/);
		return num.toFixed(Math.max(0, (m[1] || '').length - m[2]));
	} else {
		return num;
	}
}

export const numberAdd = (arg1, arg2) => {
	arg1 = Number(arg1) || 0;
	arg2 = Number(arg2) || 0;
	arg1 = toNonExponential(arg1);
	arg2 = toNonExponential(arg2);
	var r1, r2, m;
	try {
		r1 = arg1.toString().split(".")[1].length;
	} catch (e) {
		r1 = 0;
	}
	try {
		r2 = arg2.toString().split(".")[1].length;
	} catch (e) {
		r2 = 0;
	}
	m = Math.pow(10, Math.max(r1, r2));
	return (numberMul(arg1, m) + numberMul(arg2, m)) / m;
}

// 减
export const numberSub = (arg1, arg2) => {
	arg1 = Number(arg1) || 0;
	arg2 = Number(arg2) || 0;
	arg1 = toNonExponential(arg1);
	arg2 = toNonExponential(arg2);
	var r1, r2, m, n;
	try {
		r1 = arg1.toString().split(".")[1].length;
	} catch (e) {
		r1 = 0;
	}
	try {
		r2 = arg2.toString().split(".")[1].length;
	} catch (e) {
		r2 = 0;
	}
	m = Math.pow(10, Math.max(r1, r2));
	// 动态控制精度长度
	n = (r1 >= r2) ? r1 : r2;
	return ((numberMul(arg1, m) - numberMul(arg2, m)) / m).toFixed(n);
}

// 乘
export const numberMul = (arg1, arg2) => {
	arg1 = Number(arg1);
	arg2 = Number(arg2);
	if ((!arg1 && arg1 !== 0) || (!arg2 && arg2 !== 0)) {
		return null;
	}
	arg1 = toNonExponential(arg1);
	arg2 = toNonExponential(arg2);
	var n1, n2;
	var r1, r2; // 小数位数
	try {
		r1 = arg1.toString().split(".")[1].length;
	} catch (e) {
		r1 = 0;
	}
	try {
		r2 = arg2.toString().split(".")[1].length;
	} catch (e) {
		r2 = 0;
	}
	n1 = Number(arg1.toString().replace(".", ""));
	n2 = Number(arg2.toString().replace(".", ""));
	return n1 * n2 / Math.pow(10, r1 + r2);
}

// 除
export const numberDiv = (arg1, arg2) => {
	arg1 = Number(arg1);
	arg2 = Number(arg2);
	if (!arg2) {
		return null;
	}
	if (!arg1 && arg1 !== 0) {
		return null;
	} else if (arg1 === 0) {
		return 0;
	}
	arg1 = toNonExponential(arg1);
	arg2 = toNonExponential(arg2);
	var n1, n2;
	var r1, r2; // 小数位数
	try {
		r1 = arg1.toString().split(".")[1].length;
	} catch (e) {
		r1 = 0;
	}
	try {
		r2 = arg2.toString().split(".")[1].length;
	} catch (e) {
		r2 = 0;
	}
	n1 = Number(arg1.toString().replace(".", ""));
	n2 = Number(arg2.toString().replace(".", ""));
	return numberMul((n1 / n2), Math.pow(10, r2 - r1));
	// return (n1 / n2) * Math.pow(10, r2 - r1);   // 直接乘法还是会出现精度问题
}

export const floatMod = (arg1, arg2) => {
	arg1 = Number(arg1);
	arg2 = Number(arg2);
	if (!arg2) {
		return null;
	}
	if (!arg1 && arg1 !== 0) {
		return null;
	} else if (arg1 === 0) {
		return 0;
	}
	let intNum = arg1 / arg2;
	intNum = intNum < 0 ? Math.ceil(arg1 / arg2) : Math.floor(arg1 / arg2); // -1.02 取整为 -1; 1.02取整为1
	let intVal = numberMul(intNum, arg2);
	return numberSub(arg1, intVal);
	12.4
}

使用库来完成

bignumber.js

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const BigNumber = require('bignumber.js');
0.1 + 0.2                       // 0.30000000000000004
x = new BigNumber(0.1)
y = x.plus(0.2)                 // '0.3'
BigNumber(0.7).plus(x).plus(y)  // '1.1'
x.plus('0.1', 8)                // '0.225'

math.js

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const math = require('math.js')
math.add(0.01, 0.02) // 0.03