Software Engineering

# How to Solve the Grouped by Commas Challenge in Javascript

## The challenge#

Finish the solution so that it takes an input `n` (integer) and returns a string that is the decimal representation of the number grouped by commas after every 3 digits.

Assume: `0 <= n < 2147483647`

Examples:

``````       1  ->           "1"
10  ->          "10"
100  ->         "100"
1000  ->       "1,000"
10000  ->      "10,000"
100000  ->     "100,000"
1000000  ->   "1,000,000"
35235235  ->  "35,235,235"
``````

## The solution in Javascript#

Option 1:

``````function groupByCommas(n) {
return n.toLocaleString()
}
``````

Option 2:

``````function groupByCommas(n) {
return n.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}
``````

Option 3:

``````function groupByCommas(n) {
var s = n.toString(),
r = [];
s = reverse(s);
for (var i = 0, l = s.length; i < l; i += 3) {
r.push(s.substr(i, 3));
}
return reverse(r.join(','));
}
function reverse(s) {
return s.split('').reverse().join('');
}
``````

## Test cases to validate our solution#

``````describe("Tests", () => {
it("test", () => {
Test.assertEquals(groupByCommas(1), '1');
Test.assertEquals(groupByCommas(10), '10');
Test.assertEquals(groupByCommas(100), '100');
Test.assertEquals(groupByCommas(1000), '1,000');
Test.assertEquals(groupByCommas(10000), '10,000');
Test.assertEquals(groupByCommas(100000), '100,000');
Test.assertEquals(groupByCommas(1000000), '1,000,000');
Test.assertEquals(groupByCommas(35235235), '35,235,235');
});
});
``````