How to document a string type in jsdoc with limited possible values

How about declaring a dummy enum:

/**
 * Enum string values.
 * @enum {string}
 */
Enumeration = {
    ONE: "The number one",
    TWO: "A second number"
};

/**
 * Sample.
 * @param {Enumeration} a one of the enumeration values.
 */
Bar.prototype.sample = function(a) {};


b = new Bar();

bar.sample(Enumeration.ONE)

You need to at least declare the enum to JSDOC, for this, though. But the code is clean and you get auto-completion in WebStorm.

The multiple files problem though cannot be solved this way.

What about:

/**
 * @typedef {"keyvalue" | "bar" | "timeseries" | "pie" | "table"} MetricFormat
 */

/**
 * @param format {MetricFormat}
 */
export function fetchMetric(format) {
    return fetch(`/matric}`, format);
}

As of late 2014 in jsdoc3 you have the possibility to write:

/**
 * @param {('rect'|'circle'|'ellipse')} shapeType - The allowed type of the shape
 */
Shape.prototype.getType = function (shapeType) {
  return this.type;
};

Of course this will not be as reusable as a dedicated enum but in many cases a dummy enum is an overkill if it is only used by one function.

See also: https://github.com/jsdoc3/jsdoc/issues/629#issue-31314808