Verifying whether an item shows potential for being a successful function

Question

Verifying whether an item shows potential for being a successful function

When using protractor.js,

I am working with functions that utilize promises/defer. For instance:

var myFunc = function(_params) {
  var deferred = protractor.promise.defer();
  /***do some magic code***/
  /****wait for other promises****/
  /*****deferred.fulfill();*****/
  return deferred.promise;
};

Is there a specific way, besides typeof statements, to determine if this function (when passed elsewhere) involves promises?

```
typeof promiseMaybe === 'function'
```
```
typeof promiseMaybe.then === 'function'
```
- && combined with the previous statement?

Alternatively, is there a different method rather than typeof, such as...

promiseMaybe.isThenable

protractor.promise.isThenable(promiseMaybe)

A Clear Explanation

I have a function that will accept myFunc as an argument, but it may also receive strings and finders. How can I determine if a parameter represents a function that involves promising something, potentially before invoking the function?

javascript types selenium-webdriver promise protractor

Answer 1

Answer №1

If you're working with Protractor, there's a convenient helper method available - protractor.promise.isPromise():

var el = element(by.css('foo'));

protractor.promise.isPromise('foo'); // Returns false
protractor.promise.isPromise(el); // Returns false
protractor.promise.isPromise(el.click()); // Returns true

This method in Protractor is directly inherited from selenium-webdriver, and you can check out the source code here:

/**
 * Determines whether a {@code value} should be treated as a promise.
 * Any object whose "then" property is a function will be considered a promise.
 *
 * @param {*} value The value to test.
 * @return {boolean} Whether the value is a promise.
 */
promise.isPromise = function(value) {
  return !!value && goog.isObject(value) &&
      typeof value['then'] === 'function';
};

In simple terms, any object that has a then method is identified as a Promise.

Answer 2

If you're working with Protractor, there's a convenient helper method available - protractor.promise.isPromise():

var el = element(by.css('foo'));

protractor.promise.isPromise('foo'); // Returns false
protractor.promise.isPromise(el); // Returns false
protractor.promise.isPromise(el.click()); // Returns true

This method in Protractor is directly inherited from selenium-webdriver, and you can check out the source code here:

/**
 * Determines whether a {@code value} should be treated as a promise.
 * Any object whose "then" property is a function will be considered a promise.
 *
 * @param {*} value The value to test.
 * @return {boolean} Whether the value is a promise.
 */
promise.isPromise = function(value) {
  return !!value && goog.isObject(value) &&
      typeof value['then'] === 'function';
};

In simple terms, any object that has a then method is identified as a Promise.

Verifying whether an item shows potential for being a successful function

When using protractor.js,

A Clear Explanation

Answer №1

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