Error: [vuex] vuex requires a Promise polyfill in this browser

An error message everyone finds himself surprised to see once you start unit testing Vue components which have a dependency to vuex:

PhantomJS 2.1.1 (Linux 0.0.0) ERROR
  Error: [vuex] vuex requires a Promise polyfill in this browser.
  at webpack:///~/vuex/dist/vuex.esm.js:96:0 <- index.js:54757

Searching the web for the error message quickly unveils a solution on Stack Overflow:

Install Babel Polyfill:

npm install --save-dev babel-polyfill

then include the polyfill file before your source and test files within the files section of your karma.conf.js:

files: [
  '../node_modules/babel-polyfill/dist/polyfill.js',
  'index.js'
],

More information and discussions about different solutions can be found in the GitHub repository of the webpack vuejs-template in issue #260 and #474.

vuejs vuex