Improve context.runtime.file when logtail is called indirectly

[gustavopch]

Suppose I have a file named utils/logging.ts containing:

export const log = (message, context) => {
  logtail.info(message, context)
}

If I import and call log('Hello') from a file named foo.js, the context.runtime.file is set to utils/logging.js. I wanted it to be foo.js instead.

[curusarn]

Hi @gustavopch,

Thank you for reaching out!
You can customize which file and function becomes part of the log context.

Here's an example of file logging.js with simple function for logging:

const { Logtail } = require("@logtail/node");
const { LogLevel } = require("@logtail/types");

module.exports = {
    log(msg) {
        const token = process.env.BETTER_STACK_SOURCE_TOKEN;
        const logtail = new Logtail(token, {level: "debug"});
        const stackContextHint = { fileName: "logging", methodNames: [ "log" ] };
        logtail.log(msg, "info", { key: "value" }, stackContextHint);
    },
};

Note that you need to use logtail.log() and pass stackContextHint as an argument.
Could you try this out and let me know if it works for you? 🙏

Thanks again for your question!

[gustavopch]

Hi @curusarn, thanks for the information. I think it's missing from the docs. I tried what you suggested, but it didn't point to the line/function that I was expecting. I ended up passing the source location manually to context. It's super simple, looks like new Error().stack?.split('\n')[3]?.trim(), and works on the browser too – by inspecting this repo, it seems @logtail/browser doesn't include that logic.

[PetrHeinz]

Hi @gustavopch, thanks for opening the issue 🙌

It's tru that there were some issues in how StackContextHint was handled at the moment. I've fixed them in #93 and added a usage example to our example project. I'm planning on mentioning it in the docs as well.

I hope it would work for you after the changes, works nicely in example project. 🙏

The reason we're not using new Error().stack in browser environment is that the output is not standardized at the moment. Each browser has slightly different syntax. Also, code used in browser env is often going through a build process and/or minification, which often makes the results unusable.

However, if new Error().stack works for your use cases, feel free to continue using it in your custom context 👍

[gustavopch]

Hi @PetrHeinz, got it, thanks for the explanation.

Also, code used in browser env is often going through a build process and/or minification, which often makes the results unusable.

FWIW, source map supported (as asked in #63) would help on this specific part.