js实现加减乘除 计算js丢失精度

js实现加减乘除 计算js丢失精度

/**
 * 公用方法
 */
/********应用于几乎所有页面************** */
/**
 * 说明：javascript的加法结果会有误差，在两个浮点数相加的时候会比较明显。这个函数返回较为精确的加法结果。  
	返回值：arg1加上arg2的精确结果  
 * @param {*加数} arg1 
 * @param {*加数} arg2 
 * @param {*是否需要格式化} needFormat 
 */
function accAdd(arg1, arg2, needFormat) {
	arg1 = parseFloat(arg1 + "");
	arg2 = parseFloat(arg2 + "");
	if (isNaN(arg1)) {
		arg1 = 0;
	}
	if (isNaN(arg2)) {
		arg2 = 0;
	}
	var result = (arg1 * 100 + arg2 * 100) / 100;
	needFormat && (result = keepDecimalFull(result, $ANumPosition));
	return parseFloat(result) === 0 ? '' : result;
}

function accSub(arg1, arg2, needFormat) {
	arg1 = parseFloat(arg1 + "");
	arg2 = parseFloat(arg2 + "");
	if (isNaN(arg1)) {
		arg1 = 0;
	}
	if (isNaN(arg2)) {
		arg2 = 0;
	}
	var result = (arg1 * 100 - arg2 * 100) / 100;
	needFormat && (result = keepDecimalFull(result, $ANumPosition));
	return parseFloat(result) === 0 ? '' : result;
}
/**
 * 乘法
 * @param {*} arg1 
 * @param {*} arg2 
 * @param {*是否需要格式化} needFormat 
 */
function accMulti(arg1, arg2, needFormat) {
	arg1 = parseFloat(arg1 + "");
	arg2 = parseFloat(arg2 + "");
	if (isNaN(arg1)) {
		arg1 = 0;
	}
	if (isNaN(arg2)) {
		arg2 = 0;
	}
	var result = arg1 * arg2;
	needFormat && (result = keepDecimalFull(result, $ANumPosition));
	return parseFloat(result) === 0 ? '' : result;
}
/**
 * 除法
 * @param {*被除数} Dividend 
 * @param {*除数} Divisor 
 * @param {*是否需要格式化} needFormat 
 * @param {*是否生成百分比} isPercent 
 * @param {*额外的小数位数保留} extraFormat 
 */
function accDiv(Dividend, Divisor, needFormat, isPercent, extraFormat) {
	Dividend = parseFloat(Dividend + "");
	Divisor = parseFloat(Divisor + "");
	var result;

	if (isNaN(Dividend)) {
		Dividend = 0;
	}
	if (isNaN(Divisor)) {
		Divisor = 0;
	}

	if (Divisor === 0) {
		result = 0;
	} else {
		if (isPercent) {
			result = Dividend * 100 / Divisor;
		} else {
			result = Dividend / Divisor;
		}
	}
	needFormat && (result = keepDecimalFull(result, extraFormat ? extraFormat : $ANumPosition));
	return parseFloat(result) === 0 ? '' : result;
}
/**
 * toFixed 四舍五入不精确 比如127.425
 * @param {*数字} num 
 * @param {*保留位数} pos 
 */
function keepDecimalFull(num, pos) {
	var result = parseFloat(num);
	var decimal;
	var pos = pos || 2;
	var pos_multiple = 100;

	// 放大倍数
	if(pos){
		pos_multiple = 10;

		for(var i = 1;i < pos;i++){
			pos_multiple *= 10;
		}
	}

	if (isNaN(result)) {
	  result = 0;
	}
	result = Math.round(num * pos_multiple) / pos_multiple;
	
	decimal = result.toString();

	// 补充小数点
	var pos_decimal = decimal.indexOf('.');
	if (pos_decimal < 0) {
	  pos_decimal = decimal.length;
	  decimal += '.';
	}
	
	while (decimal.length <= pos_decimal + pos) {
		decimal += '0';
	}
	return decimal;
}