**Approach** -> String is considered as divisor , when the lengths of both strings str1 and str2 is divisible by substring length and on repetition of substring should be able to get both strings str1 and str2 , following greedy approach and start with the string which is having less length in str1 and str2

**Javascript Code**

```
/**
* @param {string} str1
* @param {string} str2
* @return {string}
*/
var gcdOfStrings = function(str1, str2) {
let len1 = str1.length;
let len2 = str2.length;
let min = Math.min(len1, len2);
const isDivisor = (l) => {
if (len1 % l !== 0 || len2 % l !== 0) {
return false;
}
let substring = str1.slice(0, l);
let f1 = len1 / l;
let f2 = len2 / l;
return substring.repeat(f1) === str1 && substring.repeat(f2) === str2;
};
for (let i = min; i > 0; i--) {
if (isDivisor(i)) {
return str1.slice(0, i);
}
}
return "";
};
```

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