Write a script using Google Apps Script (javascript)

My small project is to have a google sheet with 3 tabs, 'New Data', 'Old Data', 'The difference Data'.What I want to do is have a script(javascript) that looks at the 'Old Data' tab, compares it to the 'New Data' tab and than populates the 3rd tab 'the difference' with all the columns of data that are in the 'new data' tab but NOT in the 'old data' tab. this script need to be run inside the script editor in google sheets ! My small project is to have a google sheet with 3 tabs, 'New Data', 'Old Data', 'The difference Data'.What I want to do is have a script(javascript) that looks at the 'Old Data' tab, compares it to the 'New Data' tab and than populates the 3rd tab 'the difference' with all the columns of data that are in the 'new data' tab but NOT in the 'old data' tab. this script need to be run inside the script editor in google sheets ! the 'new data' has 10 colums, the 'old data' has 8 columns, both the 'new data' and the 'old data' have a common column titled 'part number', the 3rd tab must look at the part numbers in the 'new data' tab compare the items to the 'old data' tab and populate the 3rd tab'the difference' with selected columns of data from the 'new data' tab.