---
title: Steamroller
---
 Remember to use <a>**`Read-Search-Ask`**</a> if you get stuck. Try to pair program  and write your own code 
###  Problem Explanation:
This problem seems simple but you need to make sure to flatten any array, regardless of the level which is what adds a bit of difficulty to the problem.
#### Relevant Links
* <a href='http://forum.freecodecamp.com/t/javascript-array-isarray/14284' target='_blank' rel='nofollow'>Array.isArray()</a>
##  Hint: 1
You need to check if an element is an array or not.
> _try to solve the problem now_
##  Hint: 2
If you are dealing with an array, then you need flatten it by getting the value inside of the array. This means if you have `[[4]]` then instead of returning `[4]` you need to return `4`. If you get `[[[4]]]` then the same, you want the `4`. You can access it with `arr[index1][index2]` to go a level deeper.
> _try to solve the problem now_
##  Hint: 3
You will definitely need recursion or another way to go beyond two level arrays to make the code flexible and not hard-coded to the answers needed. Have fun!
> _try to solve the problem now_
## Spoiler Alert!
**Solution ahead!**
##  Basic Code Solution:
function steamrollArray(arr) {
var flattenedArray = [];
// Create function that adds an element if it is not an array.
// If it is an array, then loops through it and uses recursion on that array.
var flatten = function(arg) {
if (!Array.isArray(arg)) {
flattenedArray.push(arg);
} else {
for (var a in arg) {
flatten(arg[a]);
}
}
};
// Call the function for each element in the array
arr.forEach(flatten);
return flattenedArray;
}
// test here
steamrollArray([1, [2], [3, [[4]]]]);
 <a href='https://repl.it/CLnh/0' target='_blank' rel='nofollow'>Run Code</a>
### Code Explanation:
* Create a new variable to keep flattened arrays.
* Create a function that will add non array elements to the new variable, and for the ones that are array it loops through them to get the element.
* It does that by using recursion, if the element is an array then call the function again with a layer of array deeper to check if it is an array or not. if it is not then push that non-array element to the variable that gets returned. Otherwise, keep going deeper.
* Invoke the function, the first time you will always pass it an array, so it always fall in to the isArray branch
* Return the flattened array.
#### Relevant Links
* <a href='http://forum.freecodecamp.com/t/javascript-array-prototype-push/14298' target='_blank' rel='nofollow'>Array.push()</a>
* <a href='http://forum.freecodecamp.com/t/javascript-array-prototype-foreach/14290' target='_blank' rel='nofollow'>Array.forEach()</a>
##  Intermediate Code Solution:
function steamrollArray(arr) {
let flat = [].concat(...arr);
return flat.some(Array.isArray) ? steamrollArray(flat) : flat;
}
flattenArray([1, [2], [3, [[4]]]]);
 <a href='https://repl.it/CLni/0' target='_blank' rel='nofollow'>Run Code</a>
### Code Explanation:
* Use spread operator to concatenate each element of `arr` with an empty array
* Use `Array.some()` method to find out if the new array contains an array still
* If it does, use recursion call `steamrollArray` again, passing in the new array to repeat the process on the arrays that were deeply nested
* If it does not, return the flattened array
#### Relevant Links
* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some' target='_blank' rel='nofollow'>Array.some</a>
* <a href='http://forum.freecodecamp.com/t/javascript-array-prototype-concat/14286' target='_blank' rel='nofollow'>Array.concat</a>
* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator' target='_blank' rel='nofollow'>Spread operator</a>
* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator' target='_blank' rel='nofollow'>Ternary Operator (`condition ? a : b`)</a>
##  Intermediate Code Solution 2:
function steamrollArray(arr) {
while(arr.some(element => Array.isArray(element))) {
arr = arr.flat();
}
return arr;
}
steamrollArray([1, [2], [3, [[4]]]]);
 <a href='https://repl.it/repls/ContentMiserlySweepsoftware' target='_blank' rel='nofollow'>Run Code</a>
### Code Explanation:
* Use `Array.some()` method to find out if the new array contains an array still, if it does flatten the array
* Repeats, until there is no more arrays inside arr.
#### Relevant Links
* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some' target='_blank' rel='nofollow'>Array.some</a>
* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat' target='_blank' rel='nofollow'>Array.flat</a>
##  Advanced Code Solution:
function steamrollArray(arr) {
return arr.toString()
.replace(',,', ',') // "1,2,,3" => "1,2,3"
.split(',') // ['1','2','3']
.map(function(v) {
if (v == '[object Object]') { // bring back empty objects
return {};
} else if (isNaN(v)) { // if not a number (string)
return v;
} else {
return parseInt(v); // if a number in a string, convert it
}
});
}
 <a href='https://repl.it/CpDy/4' target='_blank' rel='nofollow'>Run Code</a>
### Code Explanation:
* First we turn the array to a string, which will give us a string of numbers seperated by a comma, double comma if there was an empty array and literal object text if there was an object, which we can fix it later in our if statement.
* We replace the double comma with one, then split it back into an array.
* map through the array and fix object values and convert string numbers to regular numbers.
##  NOTES FOR CONTRIBUTIONS:
*  **DO NOT** add solutions that are similar to any existing solutions. If you think it is **_similar but better_**, then try to merge (or replace) the existing similar solution.
* Add an explanation of your solution.
* Categorize the solution in one of the following categories — **Basic**, **Intermediate** and **Advanced**. 
> See  <a href='http://forum.freecodecamp.com/t/algorithm-article-template/14272' target='_blank' rel='nofollow'>**`Wiki Challenge Solution Template`**</a> for reference.