Defining type of parameter for the directive

Question

How to define the types of parameters for the directive in angularjs? What type to use for & binding?

See ngdoc or jsdoc in example code.

UPD: My goal is to get answers on below questions

 * @param {<< what to write here? >>} parentContextExpression
 * @param {<< what to write here? >>} oneWayParameter

angular.module('app', [])
  .directive('exampleDir', exampleDir);

/**
 * @ngdoc directive
 * @module app
 * @name app.directive:exampleDir
 * @param {<< what to write here? >>} parentContextExpression
 * @param {<< what to write here? >>} oneWayParameter
 * @param {Object=} twoWayParameter
 * @usage
 * <example-dir
 *   parent-context-expression="externalFn()"
 *   one-way-parameter="parentScopeVariable"
 *   two-way-parameter="parentScopeObject"
 * ></example-dir>
 **/
function exampleDir() {
  return {
    template: '...',
    scope: {
      parentContextExpression: '&',
      oneWayParameter: '@',
      twoWayParameter: '="
    }
  }
}

Answer 1

If you have a look at the Angular Material code you will see the source of this answer.

Here's a simplified version that looks more like the source in the question.

/**
 * @ngdoc directive
 * @name exampleDir
 *
 * @param {string} one-way-parameter A One way.
 * @param {expression=} parent-context-expression An Expression
 */
function ExampleDir() {
  return {
    restrict: 'E',

    scope: {
      oneWayParameter: '@?oneWayParameter',
      parentContextExpression: '=?parentContextExpression'
    },
}

According to my experience with the Closure Compiler (which is not the same as JSDoc, nor is it ngDoc):

The type of scope is {Object<string>}.

The values of scope params don't exist until $onInit is run on the controller's class, so they must be nullable in the constructor. You could provide those types like this;

class SomeCtrl {
  constructor() {
    /** @type {?boolean} */
    this.oneWayParameter;
  }

  $onInit() {
    this.oneWayParameter = 'this is not a boolean';
  }
}

In this example this.oneWayParameter = 'this is not a boolean'; throws an error in Closure because the property expects a boolean, but finds a string.