JSLint
CodeClimate
ESLint
Codacy
SensioLabs Insight
CodeFactor.io
SonarQube
Source-Navigator NG
CodeSandbox
CodePen
replit
JSFiddle
StackBlitz
GitHub
Visual Studio Code
JS Bin
JSLint CodeSandboxBased on our record, CodeSandbox seems to be a lot more popular than JSLint. While we know about 300 links to CodeSandbox, we've tracked only 4 mentions of JSLint. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
UPDATE 8/22/2011: found http://jshint.com, it looks much better than http://jslint.com/. Source: about 2 years ago
Use https://jslint.com to find the unescaped quote or whatever that's invalidating the file. Remember to put quote marks in dialogue as \". Source: over 2 years ago
Ooh! I'm pretty sure I actually know this one! I watched a bunch of Douglas Crockford talk's at Yahoo! Talking about the weirdness of the language he helped develop (such as this one). He also has built JSLint to help pull out code that runs but can have unexpected results. Booleans in JS evaluate if something is truthy or falsy and undefined is falsy (19:20), however a string of "undefined" would be truthy, and... Source: over 2 years ago
For future, just pop your code into an HTML Validator, a JS Linter, or a CSS Linter and it will check for basic stuff like this. There are also plugins in most IDEs for these kind of things which are incredibly useful. Source: about 3 years ago
Ok last but not least, Codesandbox. This is a newcomer to online collaborative workspaces which seems much more advanced. Codesandbox.io allows you to create node/npm projects, install packages, setup webpack or bundlers, include frameworks like React or Vue, and code in Typescript or JavaScript. It looks and acts like an IDE (VSCode) in the cloud, allowing shareable projects, not just code snippets. - Source: dev.to / about 2 months ago
Codesandbox.io — Online Playground for React, Vue, Angular, Preact, and more. - Source: dev.to / 3 months ago
Sync your projects effortlessly with GitHub. Codesandbox. - Source: dev.to / 3 months ago
Use online code editors such as Codesandbox or Stackblitz. They let you focus on writing code rather than dealing with local environment complexities. - Source: dev.to / 3 months ago
For this article, I will be using an online code editor called Codesandbox. You can go ahead and use it as well, you can also create normal React js application on your computer. - Source: dev.to / 4 months ago
CodeClimate - Code Climate provides automated code review for your apps, letting you fix quality and security issues before they hit production. We check every commit, branch and pull request for changes in quality and potential vulnerabilities.
CodePen - A front end web development playground.
ESLint - The fully pluggable JavaScript code quality tool
replit - Code, create, andlearn together. Use our free, collaborative, in-browser IDE to code in 50+ languages — without spending a second on setup.
Codacy - Automatically reviews code style, security, duplication, complexity, and coverage on every change while tracking code quality throughout your sprints.
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.