Alter Javascript file using PHP - (R)

This is a rehearsal task to find a part time/fulltime developer for long term. Task required ability to build an algorithm & sufficient implementation skills. You will write a php method to: * get a javascript file, * alter javascript file to add a line of code to a proper position, * save file to specified path Following items should be considered while writing the code: * Injection should not corrupt the integrity of the javascript file * File content is changing almost every week * Marker is not always in the same position of the file Prototype and target javascript are included to the task.