A software regression is a software bug which makes a feature to stop functioning as intended after a certain event, for example a system upgrade, system patching.

One approach to avoiding this kind of problem is regression testing.

References

• https://en.wikipedia.org/wiki/Software_regression
• https://en.wikipedia.org/wiki/Regression_testing
• http://stackoverflow.com/questions/3464629/what-does-regression-test-mean

Functions that operate on other functions, either by taking them as arguments or by returing them, are called higher order functions.

References

• http://eloquentjavascript.net/05_higher_order.html#p_18CYJsdOxo
• https://www.sitepoint.com/higher-order-functions-javascript/
• https://medium.com/javascript-scene/the-rise-and-fall-and-rise-of-functional-programming-composable-software-c2d91b424c8c

NODE_ENV is an environment variable made popular by the Express.js framework. It is specifically used to state whethere a particular environment is production or development.

var environment = process.env.NODE_ENV

References

• http://stackoverflow.com/questions/16978256/what-is-node-env-in-express

In Node.js, you can retrieve environment variables by key from process.env object.

node -p process.env
node -p process.env.HOME

References

• http://stackoverflow.com/questions/15058954/node-js-is-there-any-documentation-about-the-process-env-variable
• https://nodejs.org/api/process.html#process_process_env
• https://davidwalsh.name/node-environment-variables

Git blame helps in viewing the line by line revision history for an entire file.

References

• https://zsoltfabok.com/blog/2012/02/git-blame-line-history/
• https://help.github.com/articles/tracing-changes-in-a-file/
• https://git-scm.com/docs/git-blame