Can some please explain this JavaScript for loop from Browserstack?

Question

I'm using BrowserStack to run my test automation - there is a config example on their site to set up 'commonCapabilities'.

I know this is basic JS but what's the use for the double pipe within this for loop?

// Code to support common capabilities
exports.config.multiCapabilities.forEach(function(caps){
  for(var i in exports.config.commonCapabilities) caps[i] = caps[i] || exports.config.commonCapabilities[i];
});

The full config:

https://www.browserstack.com/automate/protractor

exports.config = {
  'seleniumAddress': 'http://hub-cloud.browserstack.com/wd/hub',

  'commonCapabilities': {
    'browserstack.user': 'xxxx',
    'browserstack.key': 'xxxx'
  },

  'multiCapabilities': [{
    'browserName': 'Chrome'
  },{
    'browserName': 'Safari'
  },{
    'browserName': 'Firefox'
  },{
    'browserName': 'IE'
  }]
};

// Code to support common capabilities
exports.config.multiCapabilities.forEach(function(caps){
  for(var i in exports.config.commonCapabilities) caps[i] = caps[i] || exports.config.commonCapabilities[i];
});

Answer 1

It's an expression that is more easily read like so:

for(var i in exports.config.commonCapabilities) {
  caps[i] = (caps[i] || exports.config.commonCapabilities[i]);
}

Which means return caps[i] if it can be converted to true; otherwise, return exports.config.commonCapabilities[i]. If caps[i] is undefined, as that's a falsey value, it'll set the variable to exports.config.commonCapabilities[i]. It's a way of making sure each is defined, otherwise fallback to some standard config.