1.0.1 • Public • Published


Determines if a number is prime, and if not, returns the factors.

IMPORTANT: This plugin was developed for PhoneGap Day EU 2017's "Creating a Modern PhoneGap Plugin" workshop as an example. This is not intended for use in production applications! There are far better and faster ways to check candidate primes!


Supported on iOS, Android, Windows, and browser platforms.

Note: iOS, Android, and Windows gain the benefit of faster computations. In order for the browser and Windows apps to remain responsive, the computations are batched in smaller portions.

Windows: When running on Windows 10, you'll need to specify the platform (e.g., cordova run windows --archs=x64)


To install, use one of two methods:

  • cordova plugin add [--save] cordova-plugin-example-isprime

  • Add the following to your config.xml:

    <plugin name="cordova-plugin-example-isprime"/>

    Note: This will retrieve the latest version of the plugin should you later remove it (or use with PhoneGap Build). You may wish to pin to a specific version using the spec attribute.


You can use one of two patterns to check if a number is prime:

  • Typical callback pattern

    cordova.plugins.kas.isPrime(win, fail, 7);
    function win(result) {
        if (result.complete) {
            if (result.isPrime) {
                console.log(result.candidate + " is prime!");
            } else {
                console.log(result.candidate + " has factors " + result.factors);
        } else {
            // calculation ongoing; progress is 0 - 100
    function fail(err) {
        console.log("error: " + err);
  • Promise pattern (if supported by the environment)

    .then(function(result) {
        if (result.isPrime) {
            console.log(result.candidate + " is prime!");
        } else {
            console.log(result.candidate + " has factors " + result.factors);
    }).catch(function(err) {
        console.log("error: " + err);
    > **Note:** If you need progress reports, pass a function as the second parameter; i.e., `cordova.plugins.kas.isPrime(7, progressFn)`

Interim and completion results passed to the success callback look like this:

    candidateNumber,                  // the requested candidate
    completeBoolean,                  // true if the calculation is complete
    factorsArray<Number>              // factors of the candidate if NOT prime
    isPrimeBoolean,                   // indicates if the candidate is prime
    progressNumber,                   // indicates progress of the calculation (0-100)

Note: do not count on intermediate progress reports being made; different platforms report at different intervals, and there may not be a report prior to the completion report.

The following errors can be thrown (when using Promises, they are propagated to your catch handler):

  • "Native promises aren't supported in this environment" — API was called using the Promise pattern, but Promises aren't available in this environment. Note: this is the only error that is actually thrown when using the Promise pattern; all others are passed to your catch handler.
  • "Success callback must be a function" — You must supply a function that can be called upon completion of the calculation when not using the Promise pattern.
  • "Failure callback must be a function" — although rare, some platforms can generate native-side errors; you need to supply a failure function to handle these errors when not using the Promise pattern.
  • "Candidate must be a positive whole number greater than 1" — Primes are not defined for any numbers less than 2.
  • "Candidate must be within JavaScript's safe integer limit of 2^53-1" — Attempting to calculate primes beyond this limit could yield incorrect results. Because of this, no calculation is attempted.
  • "Candidate must be an integer" — Primes are only defined for whole numbers.
  • "JSON Exception; check that the JS API is passing the right result object" (Android) — This error should never occur. If it does, please contact the plugin developer.

Important Notes

  • Calculations are processed in background threads on iOS and Android. These calculations do not stop if the webview is navigated. This is left as an exercise to the reader.
  • Calculations on the Browser platform are much slower in order to avoid blocking the webview.
  • Be careful with the size of primes passed; you may end up with a computation that takes quite some time.
  • Do remember — this plugin can't check primality of any number greater than 2^53-1.


You can run the tests by executing the following commands:

$ npm run test:android
$ npm run test:browser
$ npm run test:ios
$ npm run test:windows

Note: You must have appropriate SDK installed in order to run the corresponding tests. If testing Windows apps, you must NOT be logged in as an administrator.



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