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Frontend Glossary

Frontend engineering · Data

JavaScript Object Notation

Also called: JSON, JSON data, Key-value pairs

A text format that represents data with curly braces and key-value pairs. Most data sent between frontend and backend, and most project config files, use it.

In detail

JSON is like a strict registration form. Every entry has a "name" and a "value," for example {"name": "Emma", "age": 18, "tags": ["new user"]}. A value can be a string, a number, a boolean, null, an array, or a nested object.

Its rules are stricter than JavaScript objects: keys and strings must use double quotes, there can't be a comma after the last item, and comments aren't allowed. When you edit config files like package.json by hand, one extra comma can stop the whole project from running.

After the frontend gets JSON from an API, it parses it into a JavaScript object to use. Pasting a real JSON response from an API to the AI is one of the most effective ways to get it to write correct code.

Developer info
Term ID
eng-json
DOM selectors
No DOM cues. This concept isn't detected directly on a page.
Priority
1 · when several match at the same level, the higher priority wins
Version
v1 · updated Sep 29, 2026