# Blog

## Using JavaScript Push Common Numbers from Two Arrays into a Third Array Posted on July 31, 2015 in Algorithms, JavaScript by Matt Jennings

```function commonIdsFromTwoArrays(arr1, arr2) {
// Array to push common IDs into
var commonIdsArr = [];

// Use a for in loop to iterate through
// elements in "arr1" and "i" starts off as "0" and
// increments all the way to "2" as "array1" which is passed in as the
// "arr1" parameter goes up to index 2
for(var i in arr1) {

// Use a for loop to through all elements in
// "arr2" and "j" starts off as "0" and goes up to
// "4" as the "array1" variable which is passed
// as the "arr2" parameter goes up to index 4
for(var j in arr2) {

// The IF STATEMENT makes the following comparisons:
// if(arr1[0] === arr2[0])
// if(arr1[0] === arr2[1])
// ...
// if(arr1[0] === arr2[4])
// if(arr1[1] === arr2[0])
// if(arr1[1] === arr2[1])
// ...
// FINAL COMPARISON: if(arr1[2] === arr2[4])
if(arr1[i] === arr2[j]) {

// If the comparison above is true
// push the "arr[i]" element into
// the "commonIdsArr" array
commonIdsArr.push(arr1[i]);
}
}
}

// Return the "commonIdsArr" and sort it
return commonIdsArr.sort();
}

var array1 = [50, 2, 102];
var array2 = [42, 5, 10, 2, 50];

// Output below is:
// [2, 50]
console.log(commonIdsFromTwoArrays(array1, array2));```