Infer label when possible

[sindresorhus]

Would be nice to infer the .label() when not specified. Can be useful in environments like Node.js or browser non-minified (development).

ow(foo, ow.string.label('foo'));

It feels moot having to define foo twice.

The current way to do this is to parse them from fn.toString(): https://stackoverflow.com/questions/1007981/how-to-get-function-parameter-names-values-dynamically

[sindresorhus]

I just realized I have a module for this: https://github.com/sindresorhus/fn-args Totally forgot about it.

[SamVerschueren]

I'm looking into this, but unless I'm totally missing something, it doesn't feel like fn-args would help here. I'm not even sure if it's possible. The reason is that fn-args (or the solution from StackOverflow) returns the parameter names of the function being invoked. Meaning that you can do fnArgs(ow) which returns ['e', 't'] (dist bundle). But what we want is the name of the variable passed in into the invocation of that function which seems a totally different thing.

[SamVerschueren]

This makes me wonder, how does power-assert do this?

[SamVerschueren]

I tried using callsites for this

const callsites = require('callsites');
const fs = require('fs');

const ow = function(value, predicate) {
	const site = callsites()[1];

	const line = site.getLineNumber();

	const content = fs.readFileSync(site.getFileName(), 'utf8').split('\n');

	console.log(content[line - 1]);
};

const x = 'foo';
const predicate = {};

ow(x, predicate);

This prints the string ow(x, predicate) where we should be able to strip out x. I was hoping this information was present in the callsite itself, but it isn't. So this solution would only work in Node because it uses fs.readFileSync.

[sindresorhus]

The above is exactly what we do in AVA too to get a nice output. I think Node.js-only is better than nothing. My main use-case is Node.js anyway. We just have to document it clearly.