function convertNum(num_str){ //参数必须为 字符串
???//科学计数法字符 转换 为数字字符， 突破正数21位和负数7位的Number自动转换
???// 兼容 小数点左边有多位数的情况，即 a×10^b（aEb），a非标准范围（1≤|a|<10）下的情况。如 3453.54E-6 or 3453.54E6
???var resValue = ‘‘,
???power = ‘‘,
???result = null,
???dotIndex = 0,
???resArr = [],
???sym = ‘‘;
???var numStr = num_str.toString();
???if(numStr[0] == ‘-‘){ ?// 如果为负数，转成正数处理，先去掉‘-’号，并保存‘-’.
???numStr = numStr.substr(1);
???sym = ‘-‘;
???}console.log(numStr)
???if ((numStr.indexOf(‘E‘) != -1) ||(numStr.indexOf(‘e‘) != -1)){ ?
???????var regExp = new RegExp( ‘^(((\\d+.?\\d+)|(\\d+))[Ee]{1}((-(\\d+))|(\\d+)))$‘,‘ig‘ );
???????result = regExp.exec(numStr);
???????console.log(result);
???????if (result != null){
??????????resValue = result[2];
??????????power = result[5];
??????????result = null;
??????}
???????if (!resValue && !power){ return false}
???????dotIndex = resValue.indexOf(‘.‘);
???????resValue = resValue.replace(‘.‘,‘‘);
???????resArr = resValue.split(‘‘); ?
???????if(Number(power) >= 0){
???????????var subres = resValue.substr(dotIndex);
???????????power = Number(power);
???????????//幂数大于小数点后面的数字位数时，后面加0
???????????for(var i=0; i<power-subres.length; i++) {
???????????resArr.push(‘0‘);
???????}
???????????if(power-subres.length < 0){
???????????resArr.splice(dotIndex+power, 0, ‘.‘);
???????????}
???????}else{
???????????power = power.replace(‘-‘,‘‘);
???????????power = Number(power);
???????????//幂数大于等于 小数点的index位置, 前面加0
???????????for(var i=0; i<=power-dotIndex; i++) {
???????resArr.unshift(‘0‘);
???????}
???????????var n = power-dotIndex >= 0 ? 1 : -(power-dotIndex);
???????????resArr.splice(n, 0, ‘.‘);
???????}
}
???resValue = resArr.join(‘‘);
?????console.log(sym+resValue);
?????return sym+resValue;
}
使用
convertNum(‘3.54545E-2‘)
js 科学计数法
原文地址：https://www.cnblogs.com/wang-z-z/p/9068595.html