pogs | Proximal Operator Graph Solver | Math library

It would help to know the actual query, that should have been part of the error message.

I assume that the problem is with

Your code compares two arrays—concretely, it keeps only those items of the first array that the second array contains.

To do so, your function justCoolStuff takes both arrays. Then it declares a function called isInSecondArray. This function is then passed to the invocation of the filter function in the line firstArray.filter(isInSecondArray).

The filter function iterates over firstArray. As it iterates, it passes each item from firstArray into the isInSecondArray function. For example, if firstArray contains five elements, then isInSecondArray will run five times, once with each item. At every iteration, the isInSecondArray function iterates over the second array and compares the item from the first array with the current item from the second array. filter then returns a new array with only those items for which isInSecondArray returned a truthy value.

In other words, you have two loops, one implicit in filter, another explicit in the for loop. The for loop is nested in the filter loop. If your arrays have five and four items, respectively, there will be a total of 4 * 5 = 20 iterations. (That number could be reduced significantly if you used sets instead of arrays, but admittedly that's not what you asked about.)

filter function reference

Maybe this can help you in the right direction: