JavaScript cookbook

My list of signup emails has duplicates.

Every button I build inside a loop calls the same handler, and each one logs the same last number.

I reload the page and every setting the user picked is gone, or the app throws an error reading yesterday's saved data.

I copy a settings object with the spread operator, change one nested field on the copy, and the original changes too.

My fetch call fails and the page just sits there blank, with nothing in the console telling me or the user what happened.

I want a script I can run from the terminal on any file, not one where I open the code and change a filename by hand.

Every time someone submits my signup form, the whole page reloads and any message I wanted to show them disappears instantly.

A method that reads this.count works fine on its own, but as soon as I pass it to addEventListener, this turns into the button.

My search box fires a network request on every single keystroke, and the results flicker before the user has even finished typing.

I add a click handler to every item when the list loads, but items added later just sit there and do nothing when clicked.

My one script.js file now handles the whole page, and finding which part broke after a small change takes longer every week.

I type fast into a search box and the results flash the wrong thing for a second because an older request answers after a newer one.

A heavy calculation just freezes the page.