Nodes.js: based on my experience where I think it fits well, ways I've used it and an over view of some ECMAScript5 and Harmony features you can use with node.js today.
the descriptors of any property Property values can be changed however var o = { a: 1 }; Object.seal(o); console.log("o is sealed? ", Object.isSealed(o)); o.b = 2; // BOOM
require('assert'); const baz = 'baz'; assert.equal('baz', baz); baz = 'new baz'; // BOOM! // SyntaxError: Assignment to constant variable. var assert = require('assert'); { var foo = 'foo'; let bar = 'bar'; } assert.equal('foo', foo); assert.equal('bar', bar); // BOOM! // ReferenceError: bar is not defined