create post route

string concatenation (the thing that happens when you do `"string" + otherThingOrAnotherString`) is slower than joining an array on an empty string: `["string", otherThingOrAnotherString].join("")`. This is because the interpreter immediately knows how big the final string will be when it joins an array, whereas with multiple concatenations it has to re-allocate memory for the string on every concetanation.