Typing man node
has this on the harmony flag:
--harmony_typeof (enable harmony semantics for typeof) type: bool default: false --harmony_scoping (enable harmony block scoping) type: bool default: false --harmony_modules (enable harmony modules (implies block scoping)) type: bool default: false --harmony_proxies (enable harmony proxies) type: bool default: false --harmony_collections (enable harmony collections (sets, maps, andweak maps)) type: bool default: false --harmony (enable all harmony features (except typeof)) type: bool default: false
So --harmony
is a shortcut to enable all the harmony features (e.g. --harmony_scoping
, --harmony_proxies
, etc.) From this blog post, it seems harmony enables new ECMAScript 6 features in the language. The reason your file won’t run without harmony is because app.js
is probably using non-backward compatible features from the new ECMAScript 6 standard (like block scoping, proxies, sets, maps, etc.)