js中的超过16位数字相加问题

方案一

 1 function sub(str1, str2) {
 2     // 补全0，并多补一位0
 3     let arr1 = null,
 4         arr2 = null
 5     if (str1.length > str2.length) {
 6         str1 = '0' + str1
 7         for (let i = str2.length; i < str1.length; i++) {
 8             str2 = '0' + str2
 9         }
10         arr1 = str1.split('')
11         arr2 = str2.split('')
12     } else {
13         str2 = '0' + str2
14         for (let i = str1.length; i < str2.length; i++) {
15             str1 = '0' + str1
16         }
17         arr1 = str1.split('')
18         arr2 = str2.split('')
19     }
20     // 注意这里arr里边保存的还是字符串，需要转成数字后再相加
21     for (let i = arr1.length - 1; i >= 0; i--) {
22         let temp = parseInt(arr1[i]) + parseInt(arr2[i])
23         arr1[i] = temp % 10
24         // 处理得到进位的结果
25         arr1[i - 1] = parseInt(arr1[i - 1]) + Math.floor(temp / 10)
26     }
27     if (arr1[0] === 0) {
28         return (arr1.join('')).substring(1)
29 
30     } else {
31         return arr1.join('')
32     }
33 }

方案二

 1 function sub(a,b){
 2     var res='', c=0;
 3     a = a.split('');
 4     b = b.split('');
 5     while (a.length || b.length || c){
 6         c += ~~a.pop() + ~~b.pop();
 7         res = c % 10 + res;
 8         c = c>9;
 9     }
10     return res.replace(/^0+/,'');
11 }