In JS, cannot declare a function as a type guard

[AlCalzone]

TypeScript Version: 3.1.0-dev.20180808

Search Terms: jsdoc type guard

Declaring a function as a type guard does not seem to work in JS.
any can be replaced with unknown but that doesn't change anything. The following example is trivial yet shows the issue:

Code

// filename: index.js

// @ts-check

/**
 * @param {any} value
 * @return {value is boolean}
 */
function isBoolean(value) {
	return typeof value === "boolean";
}

// Errors here:
// @return {value is boolean}
//                ~~ "}" expected (sometimes)
//          ~~~~~ the name "value" was not found

/** @param {any} val */
function foo(val) {
	if (isBoolean(val)) {
		val; // still has type `any`
	}
}

Expected behavior:

• No error at the @returns tag
• inside the if-branch, val is of type boolean

Related Issues: #25127