console.log inconsistent with JSON.stringify

问题

I have reason to believe console.log and JSON.stringify can produce inconsistent views of the same object even if it was created in a straightforward manner (see notes).

Situation

In both Google Chrome developer tools and Firebug, I had an object obj which console.log printed out as { players: {0: ...}, ...}, while JSON.stringify reported { players: {}, ...}. obj.players was {} under both functions, so it seems that console.log is the culprit. Could it be asynchronous/non-deterministic in some way?

Additional notes

I'm afraid I won't be able to provide much more context, since the code is lengthy and for a client, but I can try if there is something that could help get to the bottom this. For the moment, I am forced to stay away from console.log for inspection.

It might be useful to know that the object is formed merely from an object literal by setting properties by hand, e.g., obj.players = {}; obj.players[0] = ....

Code

A sample of what I mean can be observed at http://jsfiddle.net/9dcJP/.

回答1:

Why don't you just use console.dir(obj) instead? Or use console.log(obj) and then click on the output / expand it?

Also when I try the following code:

var obj = {};
obj.players = {};
obj.players[0] = {color: "green"};
obj.players[1] = {color: "blue"};
obj.world = "xyz";
console.log(JSON.stringify(obj));

I always (Firefox, Chrome, Opera) get this as output:

{"players":{"0":{"color":"green"},"1":{"color":"blue"}},"world":"xyz"}

Furthermore it looks like your players object is actually an array. So you should better create it as such.

Update: I just saw that you added a link to a JSFIDDLE demo, which empties the players object right after logging it. To my knowledge all web dev tools use some kind of asynchronous display, which results in an empty players object when using console.log(obj) or console.dir(obj). Firebug thereby offers the best results by displaying the object correctly using console.dir(obj).

回答2:

To answer the question - yes, console.log operations are asynchronous so can't be relied upon to print accurate values in the console - especially if you modify the printed object straight after the console.log call (like you are doing).

If you take away the line:

obj.players = {};

then both the differences between the plain console.log and the JSON.stringify dissappear.

Bearing in mind that there is a difference between logging a real object in a developer tools console (console.log(obj) and printing the stringified version of the object (console.log(JSON.stringify(obj))). So the representation of the object will still be different.

来源：https://stackoverflow.com/questions/8733802/console-log-inconsistent-with-json-stringify