native-class-ext/lib/NumberExt.js

js原生对象增加常用方法

(function(){
	const defineProperty = require('./defineProperty.js')
	
	/**
	 * 对Number类进行扩展 
	 * @author gwl
	 * @since 2020年5月8日13:04:41
	 * js进行计算时有时会出现小数点导致计算错误，如
	 * 	0.1+0.2=0.30000000000000004
	 * 	0.3-0.2=0.09999999999999998
	 * 	0.1*3=0.30000000000000004
	 * 	2.4/0.8=2.9999999999999996
	 *  解决方法：转成整数计算
	 * */
	function init(){
		/**
		 * 加
		 * @param {Number} augend 被加数
		 * @return this+augend
		 * */
		defineProperty(Number.prototype, '$add', add)
		/**
		 * 减
		 * @param {Number} subtrahend 被减数
		 * @return this-subtrahend
		 * */
		defineProperty(Number.prototype, '$subtract', subtract)
		/**
		 * 乘
		 * @param {Number} multiplicand 乘数
		 * @return this*multiplicand
		 * */
		defineProperty(Number.prototype, '$multiply', multiply)
		/**
		 * 除
		 * @param {Number} divisor 
		 * @param {Number} scale 保留小数位数
		 * @param {Number} roundingMode 舍入方式
		 * @return this/multiplicand
		 * */
		defineProperty(Number.prototype, '$divide', divide)
		/**
		 * 设置精度
		 * @param {Number} scale 小数位数，默认2
		 * @param {Number} roundingMode 舍入方式，默认Number.$ROUND_HALF_UP
		 * */
		defineProperty(Number.prototype, '$setScale', setScale)
	}
	
	/** 进位, 1.01->1.1、-1.01->-1.1 */
	defineProperty(Number, '$ROUND_UP', 0)
	/** 舍弃, 1.01->1.0、-1.01->-1.0 */
	defineProperty(Number, '$ROUND_DOWN', 1)
	/** 常规四舍五入 */
	defineProperty(Number, '$ROUND_HALF_UP', 4)
	
	function add(augend){
		const [num1, num2] = getEqScale(this, augend);
		const res = parseInt(num1.numStr) + parseInt(num2.numStr);
		return addPoint(res, num1.scale);
	}
	
	function subtract(subtrahend){
		const [num1, num2] = getEqScale(this, subtrahend);
		const res = parseInt(num1.numStr) - parseInt(num2.numStr);
		return addPoint(res, num1.scale);
	}
	
	function multiply(multiplicand){
		const num1 = getNumberInfo(this);
		const num2 = getNumberInfo(multiplicand);
		let res = parseInt(num1.numStr) * parseInt(num2.numStr);
		return addPoint(res, num1.scale + num2.scale);
	}
	
	function divide(divisor, scale=2, roundingMode=Number.$ROUND_HALF_UP){
		const [num1, num2] = getEqScale(this, divisor);
		let res = parseInt(num1.numStr) / parseInt(num2.numStr);
		return res.$setScale(scale, roundingMode);
	}
	
	function setScale(scale=2, roundingMode=Number.$ROUND_HALF_UP){
		let no, res;
		switch(roundingMode){
			//常规四舍五入
			case Number.$ROUND_HALF_UP: return parseFloat(this.toFixed(scale));
			//舍弃
			case Number.$ROUND_DOWN: 
				ni = getNumberInfo(this);
				if(ni.scale == 0) return this;
				res = ni.numSplit[0] + '.' + ni.numSplit[1].slice(0, scale);
				return parseFloat(res);
			//进位
			case Number.$ROUND_UP: 
				ni = getNumberInfo(this);
				if(ni.scale == 0) return this;
				let scaleAfter = ni.numSplit[1].slice(scale);//, scale+1
				if(scaleAfter) scaleAfter = parseInt(scaleAfter);
				res = parseInt(ni.numSplit[0] + ni.numSplit[1].slice(0, scale));
				if(scaleAfter>0) {
					if(this>0) res++;
					else if(this<0) res--;
				}
				return addPoint(res, scale);
		}
	}
	
	/**
	 * 去小数点，并保证小数点移动位数相同
	 * */
	function getEqScale(num1, num2){
		num1 = getNumberInfo(num1);
		num2 = getNumberInfo(num2);
		const masScale = Math.max(num1.scale, num2.scale);
		addZeroEnd(num1, masScale);
		addZeroEnd(num2, masScale);
		return [num1, num2];
	}
	
	/**
	 * 解析数字信息
	 * @return {Object} 
	 * 	num {Number} 原数字
	 * 	numSplit {Array} 根据小数点拆成数组
	 * 	scale {Number} 小数点后位数
	 * 	numStr {String} 去小数点后字符串
	 * */
	function getNumberInfo(num){
		let numStr = num.toString();
		const numSplit = numStr.split(".");
		let scale = 0;
		if(numSplit.length===2) {
			scale = numSplit[1].length;
			numStr = numSplit[0] + numSplit[1];
		}
		return {
			num,
			numSplit, 
			scale, 
			numStr
		};
	}
	
	/**
	 * 在尾部添加0
	 * */
	function addZeroEnd(numInfo, scale){
		const offset = scale-numInfo.scale ;
		if(offset > 0){
			numInfo.scale = scale;
			numInfo.numStr = numInfo.numStr + '0'.padEnd(offset, '0');
		}
	}
	
	//添加小数点, addPoint(123, 2) = 1.23
	function addPoint(num, scale=0){
		if(scale === 0){
			return num;
		}
		let isMinus = false
		if(num < 0) {
			isMinus = true
			num = Math.abs(num)
		}
		let str = num.toString().padStart(scale, '0');
		let res = str.slice(0, -scale);
		if(!res){
			res = '0';
		}
		let temp = str.slice(-scale);
		if(temp){
			res += '.' + temp;
		}
		res = parseFloat(res);
		if(isMinus) {
			res = 0-res
		}
		return res;
	}
	
	init();
})()