docs: mention ContextBuilder returned from #check()

[fedeci]

Description

We mention in the docs that ContextBuilder is exposed in the result of #check() middleware.

This allows to get the properties of the builder.
It can be used to create a library based on the context that will be built.
(e.g. swagger docs generation)

I don't know if it is better to expose the properties in this way or to build a "local" context, @gustavohenke what do you think?

To-do list

• I have added tests for what I changed.

• This pull request is ready to merge.

[coveralls]

Coverage remained the same at 100.0% when pulling 939bae6 on fedeci:get-builder-properties into 690cd63 on express-validator:master.

[gustavohenke]

I don't know if it is better to expose the properties in this way or to build a "local" context

Hmm I don't mind either way at the moment. The Context interface is quite small, so this looks reasonable for now.

I don't recall if the .builder property is exposed/documented anywhere... do you think it would make more sense to put it in

express-validator/src/chain/context-handler.ts

Lines 5 to 9 in 7f15d2d

	export interface ContextHandler<Chain> {
	bail(): Chain;
	if(condition: CustomValidator | ValidationChain): Chain;
	optional(options?: Partial<Optional> | true): Chain;
	}

instead?

[fedeci]

Yes, for example in check it is exposed here.
Maybe we should just document this so that the end user could create his own context with all his methods and not only access properties through the builder.

express-validator/src/middlewares/check.ts

Lines 32 to 40 in 7f15d2d

	return Object.assign(
	middleware,
	bindAll(runner),
	bindAll(new SanitizersImpl(builder, middleware as any)),
	bindAll(new ValidatorsImpl(builder, middleware as any)),
	bindAll(new ContextHandlerImpl(builder, middleware as any)),
	{ builder },
	);
	}

[gustavohenke]

Will LGTM if we can add more docs than just this 😬

• API entry
• Possibly an entry under "Features", if it's necessary to showcase more of it

[gustavohenke]

...did you want to address the previous review?

[fedeci]

Oops nope, asked review for the wrong PR😄