Improving Browser Compatibility

[WillianAgostini]

Hi, unfortunately, we currently do not support running in the browser.

We discussed removing child_process, which is used to run system commands from cron by providing a string instead of a function (IIRC).

There's an old PR related to this issue, but it is outdated.

We would gladly accept a similar PR that would disable the system commands feature in the browser environment.

Originally posted by @sheerlox in #538

Currently, node-cron call child_process for executing system commands when a string or object is provided instead of a function.

https://github.com/kelektiv/node-cron/blob/main/src/job.ts#L175-L196

To improve browser compatibility, we could refactor the import of child_process so that it is only required when actually needed. Specifically, we can introduce a validation mechanism to ensure that system commands (string or object formats) are executed only in non-browser environments.

Proposed Solution

Modify the _fnWrap function to include a browser check before requiring child_process:

private _fnWrap(cmd: CronCommand<C, boolean>): CronCallback<C, boolean> {
	switch (typeof cmd) {
		case 'function': {
			return cmd;
		}

		case 'string': {
			if (this.isBrowser)
				throw new Error('System commands are not supported in the browser.');

			const { spawn } = require('child_process');
			const [command, ...args] = cmd.split(' ');

			return spawn.bind(undefined, command ?? cmd, args, {}) as () => void;
		}

		case 'object': {
			if (this.isBrowser)
				throw new Error('System commands are not supported in the browser.');

			const { spawn } = require('child_process');
			return spawn.bind(
				undefined,
				cmd.command,
				cmd.args ?? [],
				cmd.options ?? {}
			) as () => void;
		}
	}
}

I’d like to submit a PR implementing this.
Additionally, we should decide on a suitable testing library for browser environments to ensure compatibility—perhaps using Jest with jsdom or a browser-focused framework like karma.

[intcreator]

thanks for bringing this to our attention! browser support is a great goal and I'd be interested to see a PR about this. we already use Jest so extending Jest for testing browser environments would be best

[sheerlox]

I was sure I answered this but looks like my comment got lost ... so here it is again:

I think we should think about removing child_process altogether. Wrapping around system commands ourselves probably shouldn't be in the scope of the library and adds unnecessary complexity.

Using it manually from the tick function is simple enough and gives users more control over it anyway, so I don't even think it is being widely used.

[sheerlox]

Looking through the issues seem to support that claim, or maybe it "just works ™️"

https://github.com/kelektiv/node-cron/issues?q=is%3Aissue%20child_process%20

[WillianAgostini]

Good point! We could introduce a breaking change to achieve this.
This way, we can support the browser without adding complexity.

What do you think, @intcreator?

[intcreator]

yeah I'm fine with removing child_process