camelcase

JavaScript's built-in APIs and most libraries use camelCase. If a codebase has both user_name and userName, you have to look up which spelling each variable uses.

The rule reports names with an underscore in the middle. Underscores at the start or the end (_private, unused_) and names in capitals (MAX_RETRIES) are allowed. Reading a property (row.first_name), a key in quotes and a name in a call (get_user()) aren't reported either, because those names often come from code you don't control.

Configure

Off by default. To turn it on:

[lint.rules]
"camelcase" = "error" # or "warn"

Every option, set to its default:

[lint.rules]
"camelcase" = ["error", {
  properties = "always", # "always" or "never"
  ignoreDestructuring = false,
  ignoreImports = false,
  ignoreGlobals = false,
  allow = [], # list of strings
}]

Examples

Reported:

const first_name = "Ada";

function full_name(user) {
  return { display_name: user.first + " " + user.last };
}

Not reported:

const MAX_RETRIES = 3;
const _cache = new Map();
const firstName = row.first_name;
const user = get_user(firstName);

function fullName(user) {
  return { displayName: user.first + " " + user.last, "sort_key": user.last };
}

Options

Option	Default	What it does
properties	"always"	"never" stops checking property names: object literal keys, class members, and a.b_c = 1.
ignoreDestructuring	false	Allow a destructured variable that keeps the property's name.
ignoreImports	false	Allow a named import that keeps the name it's exported with.
ignoreGlobals	false	Allow the global variables that your config or a /* global */ comment declares.
allow	[]	Names to allow. Each entry is a name or a regular expression.

const body = { user_id: 7 };
body.created_at = Date.now();

With ignoreDestructuring, only the variable with the same name as the property is allowed. A new name is still checked:

const { user_id } = await response.json();

const { id: user_id } = await response.json();

import { unstable_cache } from "next/cache";

ignoreDestructuring and ignoreImports only cover the line that creates the variable. Using it later is still reported, except where it's called or passed as an argument:

const { user_id } = await response.json();
console.log(user_id);
const key = "user:" + user_id;

import { unstable_cache } from "next/cache";
export const cache = unstable_cache;

/* global api_key */
const key = api_key;

const user_id = 7;

class Form {
  UNSAFE_componentWillMount() {}
}