Iterate over an object in Google Apps script

With V8 runtime:

var dict = {
  "foo": "a",
  "bar": "b"
};

for (const [key, value] of Object.entries(dict)) {
  Logger.log(`${key}: ${value}`);
}

I usually do something like that :

var dict = {
    "foo": "a",
    "bar": "b"
};

function showProperties(){
  var keys = [];
  for(var k in dict) keys.push(k+':'+dict[k]);
  Logger.log("total " + keys.length + "\n" + keys.join('\n'));
}

result in Logger :

You get the logger in the script editor/view/Logs