Compare values safely

I need to check whether user input equals a stored config value without misclassifying 0, '', null or NaN. Compare the two values so the result is true only when they are the same value and same type, not just loosely equal. If the values are objects or arrays, treat them as unequal unless they reference the exact same object. Use concise code I can paste into a validation function used on form submit.

Before I add this comparison into the login flow, make the outcome easy for reviewers to see. Put the strict equality result at the top of the snippet, comment why === is chosen over ==, and flag the cases that commonly confuse reviewers: 0 versus '0', null versus undefined, NaN behaviour. Make the code two or three lines max and readable for a junior dev.

I just used == to compare an input value and a stored preference and it returned true when the input was an empty string and the preference was 0. Priya on QA will call this a bug because empty string isn’t a valid numeric choice. I’m unsure whether to change all comparisons to === or adjust upstream parsing. What’s the likely cause and the safest next step for production code?

Across several projects we keep patching bugs where == accepts unintended inputs: form fields, query params, feature flags. It eats review time and surfaces in production as wrong behaviour. Which habit change will stop this recurring issue: always coerce inputs first, always use strict equality, add a lint rule, or a combination? Recommend the single best practice and how to make it stick in our team.