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ESLint is a tool for identifying and reporting on patterns found in ECMAScript/JavaScript code. In many ways, it is similar to JSLint and JSHint with a few exceptions:
* ESLint uses [Espree](https://github.com/eslint/espree) for JavaScript parsing.
* ESLint uses an AST to evaluate patterns in code.
* ESLint is completely pluggable, every single rule is a plugin and you can add more at runtime.
**Note:** `eslint --init` is intended for setting up and configuring ESLint on a per-project basis and will perform a local installation of ESLint and its plugins in the directory in which it is run. If you prefer using a global installation of ESLint, any plugins used in your configuration must also be installed globally.
The names `"semi"` and `"quotes"` are the names of [rules](http://eslint.org/docs/rules) in ESLint. The number is the error level of the rule and can be one of the three values:
The three error levels allow you fine-grained control over how ESLint applies rules (for more configuration options and details, see the [configuration docs](http://eslint.org/docs/user-guide/configuring)).
## Sponsors
* Development is sponsored by [Box](https://box.com)
I do like JSHint. And I like Anton and Rick. Neither of those were deciding factors in creating this tool. The fact is that I've had a dire need for a JavaScript tool with pluggable linting rules. I had hoped JSHint would be able to do this, however after chatting with Anton, I found that the planned plugin infrastructure wasn't going to suit my purpose.
### I'm not giving up JSHint for this!
That's not really a question, but I got it. I'm not trying to convince you that ESLint is better than JSHint. The only thing I know is that ESLint is better than JSHint for what I'm doing. In the off chance you're doing something similar, it might be better for you. Otherwise, keep using JSHint, I'm certainly not going to tell you to stop using it.
ESLint is slower than JSHint, usually 2-3x slower on a single file. This is because ESLint uses Espree to construct an AST before it can evaluate your code whereas JSHint evaluates your code as it's being parsed. The speed is also based on the number of rules you enable; the more rules you enable, the slower the process.
Despite being slower, we believe that ESLint is fast enough to replace JSHint without causing significant pain.
Yes. Since we are solving the same problems, ESLint and JSCS teams have decided to join forces and work together in the development of ESLint instead of competing with each other. You can read more about this in both [ESLint](http://eslint.org/blog/2016/04/welcoming-jscs-to-eslint) and [JSCS](https://medium.com/@markelog/jscs-end-of-the-line-bc9bf0b3fdb2#.u76sx334n) announcements.
### So, should I stop using JSCS and start using ESLint?
Not yet. We are still working to smooth the transition. You can see our progress [here](https://github.com/eslint/eslint/milestones/JSCS%20Compatibility). We’ll announce when all of the changes necessary to support JSCS users in ESLint are complete and will start encouraging JSCS users to switch to ESLint at that time. Meanwhile, we recommend you to upgrade to JSCS 3.0 and provide feedback to the team.
Yes, ESLint natively supports parsing JSX syntax (this must be enabled in [configuration](http://eslint.org/docs/user-guide/configuring).). Please note that supporting JSX syntax *is not* the same as supporting React. React applies specific semantics to JSX syntax that ESLint doesn't recognize. We recommend using [eslint-plugin-react](https://www.npmjs.com/package/eslint-plugin-react) if you are using React and want React semantics.
ESLint has full support for ECMAScript 6. By default, this support is off. You can enable ECMAScript 6 support through [configuration](http://eslint.org/docs/user-guide/configuring).
ESLint doesn't natively support experimental ECMAScript language features. You can use [babel-eslint](https://github.com/babel/babel-eslint) to use any option available in Babel.
