RegeneratorRuntime is not defined

Question

I am trying to run Karma-babel-preprocessor and a straight forward ES6 generator:

//require('babel/polyfill');

  describe("how Generators work", function() {
    it("will allow generator functions", function() {
      /*function * numbers() {
        yield 1;
        yield 2;
        yield 3;
      };*/


      let numbers = {
        [Symbol.iterator]:function*(){
            yield 1;
            yield 2;
            yield 3;
          }
      }

      let sum = 0;

      for(n of numbers){
        sum += n;
      }

      expect(sum).toBe(6);
    });
  });

From this I generated my test files (ES6 => ES5) with babel:

babel src --watch --out-dir tests

Then I run karma start I get error:

ReferenceError: regeneratorRuntime is not defined".

Relevant bits in karma.conf.js:

  // list of files / patterns to load in the browser
    files: [
      'test-main.js',
      {pattern: 'tests/*.js', included: true}
    ],


    // list of files to exclude
    exclude: [
    ],


    // preprocess matching files before serving them to the browser
    // available preprocessors: https://npmjs.org/browse/keyword/karma-preprocessor
    preprocessors: {
            'src/*.js': ['babel']
    },
        'babelPreprocessor': {
      options: {
        sourceMap: 'inline'
      },
      filename: function(file) {
        return file.originalPath.replace(/\.js$/, '.es5.js');
      },
      sourceFileName: function(file) {
        return file.originalPath;
      }
    },


// test results reporter to use
// possible values: 'dots', 'progress'
// available reporters: https://npmjs.org/browse/keyword/karma-reporter
reporters: ['progress'],

Full project on github

I am able to use many ES6 features including arrows. Just no go on Generators.

Answer 1

Node js Env - updated December 2015

This question has already been answered, please see accepted answer UNLESS running within NodeJS environment.

If like myself, you had the same error message: 'ReferenceError: regeneratorRuntime is not defined' but were running Babel within a NodeJS environment, then simply doing the following will likely solve your problem:

npm install babel-polyfill --save

Then insert the following require statement towards the top of the affected module to obtain required (generator) behaviour:

require("babel-polyfill");

This should be all you need, just importing the module adds required polyfill behaviour at runtime.

Answer 2

Similar to the post by arcseldon, I was running Babel within a NodeJS environment and getting the same error message 'ReferenceError: regeneratorRuntime is not defined'. While installing babel-polyfill does work, I went with @babel/plugin-transform-runtime instead.

@babel/plugin-transform-runtime

It needs to be installed in two ways ... first as a dev dependency:

npm install --save-dev @babel/plugin-transform-runtime

and second as a production dependency:

npm install --save @babel/runtime

And then there needs to be one simple addition to your .babelrc file:

{
  "plugins": ["@babel/plugin-transform-runtime"]
}

These additions give ES6 authoring functionality without the ReferenceError.