js中的超过16位数字相加问题

方案一

 function sub(str1, str2) {
     // 补全0，并多补一位0
     let arr1 = null,
         arr2 = null
     if (str1.length > str2.length) {
         str1 = '0' + str1
         for (let i = str2.length; i < str1.length; i++) {
             str2 = '0' + str2
         }
         arr1 = str1.split('')
         arr2 = str2.split('')
     } else {
         str2 = '0' + str2
         for (let i = str1.length; i < str2.length; i++) {
             str1 = '0' + str1
         }
         arr1 = str1.split('')
         arr2 = str2.split('')
     }
     // 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
     for (let i = arr1.length - 1; i >= 0; i--) {
         let temp = parseInt(arr1[i]) + parseInt(arr2[i])
         arr1[i] = temp % 10
         // 处理得到进位的结果
         arr1[i - 1] = parseInt(arr1[i - 1]) + Math.floor(temp / 10)
     }
     if (arr1[0] === 0) {
         return (arr1.join('')).substring(1)

     } else {
         return arr1.join('')
     }
 }

方案二

 function sub(a,b){
     var res='', c=0;
     a = a.split('');
     b = b.split('');
     while (a.length || b.length || c){
         c += ~~a.pop() + ~~b.pop();
         res = c % 10 + res;
         c = c>9;
     }
     return res.replace(/^0+/,'');
 }

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