Javascript console.log(对象)vs.连接字符串

I'm running this in node.js:

我在node.js:

> x = { 'foo' : 'bar' }
{ foo: 'bar' }
> console.log(x)
{ foo: 'bar' }
undefined
> console.log("hmm: " + x)
hmm: [object Object]
undefined
> x