Javascript

Chrome extensions live in a weird middle ground. They’re not normal web pages, but they’re not fully trusted native apps either. That matters a lot for CORS. If you build extensions long enough, you hit this fast: fetch() works in your background service worker the same request fails in a content script adding Access-Control-Allow-Origin to your request does nothing people tell you to “just use host_permissions” and then preflights still surprise you The mental model that has saved me the most time is this: ...

If you try to call the BigCommerce REST Management API directly from browser JavaScript, you’re going to hit a wall. Not because your fetch() code is wrong, but because CORS is doing exactly what it’s supposed to do. BigCommerce has multiple API surfaces, and they do not behave the same way from a browser. That distinction matters: Storefront APIs are designed for browser-facing use cases Management APIs are meant for trusted server-side access CORS policy decides whether the browser will even allow your frontend code to read the response That’s the part people usually miss. The request may leave the browser just fine, but if the response doesn’t include the right CORS headers, your app still fails. ...

If you build internal tools with Appsmith, you will hit CORS sooner or later. Usually it happens like this: your API works fine in Postman or curl, then Appsmith tries to call it from the browser and everything blows up with a vague “blocked by CORS policy” error. That is not Appsmith being weird. That is the browser enforcing cross-origin rules exactly as designed. This guide is the copy-paste version I wish more teams had. No fluff, just what matters for Appsmith apps. ...

Telegram bot webhooks and CORS are a weird combo, mostly because people often try to solve the wrong problem. Here’s the blunt version: Telegram does not care about CORS when delivering webhooks to your server. Browsers care about CORS. Telegram is not a browser. So if your bot backend receives webhook requests from Telegram, CORS is irrelevant for that inbound traffic. Where CORS does matter is when you put a browser app in front of your bot infrastructure and that browser tries to call your webhook endpoint, bot API proxy, status endpoint, or admin interface. ...

CORS gets blamed for a lot of things it didn’t do. Half the time the server is fine and the browser is blocking access on purpose. The other half, someone added mode: "no-cors" and made the problem harder to debug. This guide is the practical version: what the browser actually gives you, what “opaque” really means, and how to make cross-origin responses readable. The short version When your frontend calls another origin, the browser decides whether JavaScript can read the response. ...

ToolJet makes it very easy to wire up APIs, databases, and internal tools fast. Then CORS shows up and ruins your afternoon. If you are building ToolJet apps that call APIs from the browser, CORS is one of those constraints you cannot brute-force away. You either design around it, proxy around it, or configure it correctly on the server. There is no frontend-only hack that “disables CORS” in production. If somebody suggests a browser extension, close the tab. ...

If you deploy APIs on Fly.io, CORS usually stops being “just a browser thing” the moment your frontend hits production. Locally, everything works. Then your app lands behind Fly Proxy, gets a custom domain, maybe a second region, and suddenly your browser starts yelling about preflights and missing Access-Control-Allow-Origin. The good news: Fly.io doesn’t make CORS unusually hard. The bad news: Fly.io also doesn’t magically solve it for you. You still need to decide where CORS lives, how strict it should be, and how it behaves across preview apps, custom domains, and edge-facing traffic. ...

Discord bot developers hit the same wall over and over: the bot works fine from Node.js, then somebody adds a web dashboard and the browser starts screaming about CORS. I’ve seen this happen with moderation bots, music bots, internal community tools, and “quick” admin panels that turned into production apps. The pattern is predictable: the bot token works on the server somebody tries to call Discord directly from frontend JavaScript preflight requests fail, or worse, the token gets exposed the team starts sprinkling Access-Control-Allow-Origin: * everywhere and hopes for the best That’s not how you want to build a Discord bot dashboard. ...

If you’re debugging “CORS errors with SendGrid webhooks,” there’s a decent chance you’re solving the wrong problem. I’ve seen teams burn hours tweaking Access-Control-Allow-Origin on webhook endpoints that were never meant to be called by a browser in the first place. SendGrid webhooks are server-to-server callbacks. CORS is a browser enforcement layer. Those are two very different worlds. The real mess usually starts when someone tries to involve frontend JavaScript in webhook flows. ...

Real-time apps make CORS weirder than plain old fetch(). A normal API request is easy to reason about: browser sends an Origin, server returns Access-Control-Allow-Origin, done. Real-time stacks like Socket.IO and SignalR add negotiation endpoints, long polling fallbacks, credentials, sticky sessions, and WebSocket upgrades. That combination creates the kind of bug where everything works locally, then production starts throwing “CORS policy blocked” while your websocket dashboard looks perfectly healthy. I’ve hit this enough times that I now treat real-time CORS as a separate problem, not just “API CORS but more.” ...