javascript - Unusual object definition -

i stumbled upon this, eyes, strange object declaration.

var config = {}; {    config.foo = 'foo';   config.bar = 'bar'; }; 

it works, though have guessed wouldn't.

confused open console in chrome devtools, , enter:

var = {}; // => undefined 

nothing strange far. enter:

{ a.b = 'b'; } // => uncaught syntaxerror: unexpected token . 

ok, hmm ... wasn't supposed work? try, without separate evaluations of statements:

var = {}; {a.b = 'b'}; // => "b" 

hmm, no syntaxerror thrown. , if evaluate a, can see defined intended.

a; // => object {b: "b"} 

what happening? i've tried google it, don't know search for, , lack kind of knowledge figure out happening. can please explain it?

to add on has been said..

in javascript, object literal:

{x: 3} 

and block:

{   console.log("hello, world!"); } 

any statement can go inside of block.

the trouble is, {x: 3} interpreted block, on own.

to make object literal far javascript concerned, have surround in parenthesis:

({x: 3}) 

that's chrome devtools whenever sees input object literal isn't surrounded. it'll make {x: 3} ({x: 3}), {y: 15, z: 'kar'} ({y: 15, z: 'kar'}), , on.

the trouble is, it'll blocks. turns {x = y} ({x = y}), of course syntax error. javascript thinks you're giving object literal, doesn't expect statement.

however, devtools ignores rule of turning un-parenthesized object literals parenthesized object literals if have statement before object literal. works:

console.log('bananas!'); {x = y} 

and statement doesn't really need statement. there needs semicolon before block:

;{x = y} 

it's weird quirk of chrome devtools. it's supposed people new coding javascript (and object literals), can confusing people are experienced!