40 columns                              |
>>> empty map
var m = { };
<<<
var m = {};
>>> exactly 40 characters
var m = {first: second, third: forth__};
<<<
var m = {first: second, third: forth__};
>>>
var m = {first: second, third: fourth, fifth: sixth};
<<<
var m = {
  first: second,
  third: fourth,
  fifth: sixth
};
>>> nested unsplit map
var m = {a: {b: c}, d: {},
    e: {f: g  }  };
<<<
var m = {a: {b: c}, d: {}, e: {f: g}};
>>> nested split map
var m = {first: 1, second: {third: fourth}, fifth: 5, nested: {sixth: seventh, eighth: nine,
    tenth: eleventh}};
<<<
var m = {
  first: 1,
  second: {third: fourth},
  fifth: 5,
  nested: {
    sixth: seventh,
    eighth: nine,
    tenth: eleventh
  }
};
>>> force multi-line because of contained block
var m = {first: 1, fn: () {"fn";},third:fourth};
<<<
var m = {
  first: 1,
  fn: () {
    "fn";
  },
  third: fourth
};
>>> containing comments
var m = {first: one /* bang */, second: two};
<<<
var m = {
  first: one /* bang */,
  second: two
};
>>> const
var map = const {"foo": "bar", "fuz": null};
<<<
var map = const {
  "foo": "bar",
  "fuz": null
};
>>> dangling comma
var map = {"foo": "bar" , };
<<<
var map = {"foo": "bar",};
>>> dangling comma multiline
var map = {"foo": "bar", "fuzzy": null , };
<<<
var map = {
  "foo": "bar",
  "fuzzy": null,
};