JavaScript Linter — Check for Common Issues
Check JavaScript code for common issues like var usage, missing semicolons, and console.log statements.
How it works
- 1Paste or type your text in the input field
- 2Click "Process" — processing happens in your browser
- 3Copy the result or download as a text file
What to do next
About JavaScript Linter
JavaScript Linter is the kind of utility you bookmark and reach for when you need it. Check JavaScript code for common issues like var usage, missing semicolons, and console.log statements. It loads quickly, works on any modern browser, and produces a result you can download or copy in a single click.
Under the hood, JavaScript Linter uses standard browser APIs to do the actual work. Input runs through the same engine, with a per-file ceiling of 0 MB so memory usage stays predictable on lower-end laptops and tablets. The engine ships as part of the page bundle, so once the page is loaded the tool keeps working even if your network connection drops.
Most people land on JavaScript Linter via a search at the moment they actually need the tool. That shapes the design: the page is a single screen with the input on one side, the controls in the middle, and the result on the other, so a first-time visitor can complete the job without reading documentation.
JavaScript Linter is structured so the question "where is my file processed?" has a single answer: in your browser tab. The engine, the controls, and the result panel are all on one page. Navigating away or closing the tab clears the page's memory the way it does for every other tab.
The only practical limit is the 0 MB per-file ceiling, which keeps the tool responsive across a wide range of devices. Run the tool ten times in a row, run it ten thousand times — it behaves the same way and produces the same quality of result.
Workflow tip: JavaScript Linter pairs well with JavaScript Formatter and JavaScript Syntax Checker. Other adjacent tools you may find useful are JavaScript Minifier and package.json Validator. Because every tool is a separate page, you can mix and match the steps that match your job. Bookmark the ones you reach for the most.
JavaScript Linter sees the most use from engineers debugging API payloads and site reliability engineers triaging logs, but the design is intentionally generic enough that you do not need a specialist background to get a good result. The defaults aim at the most common case so a first-time user can get the right output without changing any settings.
Output handling is intentionally boring: JavaScript Linter produces a single output file and triggers your browser's standard "save" behaviour. If you have a default download folder configured, that is where it will land. There is no Favtoo-side history of jobs you have run.
Some notes on the design of JavaScript Linter. The page is intentionally narrow: one input, the controls relevant to the task, and one output. Adding unrelated features would make the common case slower for the majority of users, so the surface is held to what people actually use.
JavaScript Linter is structured around the idea that a useful tool should be its own page. Open the page, do the work, close the tab — the page is the entire product. There is no onboarding flow because there is nothing to onboard into.
Tips from users who reach for JavaScript Linter regularly: process one input first to confirm the settings produce what you expect before committing to a batch; treat the page as the working surface and avoid leaving large jobs running in a backgrounded tab where the browser may throttle JavaScript; and if a particular file fails, check whether the source is intact by opening it in its native viewer — most "tool errors" are actually input errors.
JavaScript Linter fits the gap where opening a desktop app feels heavy and writing a script feels overkill. The page handles the common developer utility task with sensible defaults so a single visit usually completes the job; for highly specialised work, a dedicated desktop application can offer more knobs to turn.
If JavaScript Linter appears to hang, the engine is almost certainly still working — large inputs simply take longer to process inside a browser than they would on a server with multi-core scheduling. For inputs near the 0 MB cap, give it up to a minute on a typical laptop before assuming something is stuck.
If JavaScript Linter solved your problem, sharing the page link with someone who has the same problem is the most useful thing you can do. The catalog grows mostly through word of mouth; visitors arriving through a recommendation tend to be the ones the tool serves best.
How it works
- 1Open JavaScript Linter in your browser. The page loads quickly and the tool is ready to use the moment it becomes interactive.
- 2Select the developer file you want to process — drag-and-drop and the file picker both work.
- 3Adjust the options to match what you need. Sensible defaults cover the most common case, so you can usually skip this step.
- 4Hit the run button. standard browser APIs does the work in your browser tab.
- 5Save the output when it is ready.
- 6Re-run with different settings as often as you want. Each run produces a fresh output and the original file on disk is never modified.
Common use cases
- Convert between data formats while wiring up an integration using JavaScript Linter.
- Format a noisy log line into something a teammate can read.
- Hash a string for a quick reproducibility check.
- Encode binary content for transport in a JSON body.
- Generate a quick fixture without leaving the browser.
- Decode a token to confirm its claims during a debugging session.
- Generate boilerplate from a single specification line.
- Inspect a regex against a test string before committing it.
- Pretty-print a minified blob during incident triage.
FAQ
What issues does it check for?
var usage, == instead of ===, console statements, debugger, alert, eval, new Array/Object, and line length.
Does it fix issues automatically?
No — it reports issues with line numbers. Use the JavaScript Formatter to fix whitespace issues.
Is it like ESLint?
It checks common patterns. For full linting with custom rules, use ESLint in your project.
Does it understand JSX?
Basic JSX is handled but dedicated JSX linting requires ESLint with appropriate plugins.
What line length limit is used?
Lines exceeding 120 characters are flagged.
Is data sent to a server?
No — processing happens in your browser.
Does JavaScript Linter work with screen readers?
JavaScript Linter uses native HTML controls wherever possible, which means keyboard navigation, focus rings, and screen-reader labels work the way the platform expects. The drop zone accepts files via the keyboard-accessible file picker as well as drag-and-drop, and result downloads use standard browser download flows. If you spot an accessibility gap, Favtoo treats it as a bug worth fixing.
What should I do if JavaScript Linter fails on my file?
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is in a supported format and that it is below 0 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.
Can I use JavaScript Linter with formats other than the defaults?
The accepted formats are listed in the upload area on the tool itself. If your input is in a format that is not directly supported, convert it first using one of Favtoo's converter tools — every Favtoo converter outputs a file that is a clean input to the next tool in the chain.
Does JavaScript Linter reduce quality of the result?
JavaScript Linter is built to preserve quality wherever the underlying developer format allows it. Operations that are mathematically lossless (e.g. structural transformations, lossless re-encoding) round-trip with no perceptible change. Operations that involve a lossy codec inevitably introduce small artefacts at the byte level, but the defaults aim at the sweet spot where output looks or sounds the same to a normal viewer or listener while still being meaningfully smaller or faster than the input.
Are there any usage limits on JavaScript Linter?
Inputs are capped at 0 MB per file, which keeps memory usage stable across phones, tablets and older laptops. You can run JavaScript Linter as often as you need; every run produces a full-quality result.
Can JavaScript Linter run inside a corporate firewall?
JavaScript Linter is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (standard browser APIs) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
Are jobs run with JavaScript Linter stored anywhere?
Favtoo keeps no copy of your file because Favtoo never receives your file. JavaScript Linter runs entirely in your browser, the input is held only in your tab's memory, and closing the tab discards it. There is no opt-in cloud history, no "recent jobs" panel synced to an account, and no server-side retention to configure — the architecture simply has nowhere for your file to be stored.
Are there any hidden fees with JavaScript Linter?
JavaScript Linter is free to use. The processing runs in your browser, which keeps the per-user cost low enough that the tool can be offered openly. The download is the same file the engine produced — you can use it for as many runs as you need.