console.log() - Web APIs 编辑

The Console method log() outputs a message to the web console. The message may be a single string (with optional substitution values), or it may be any one or more JavaScript objects.

Note:

Syntax

console.log(obj1 [, obj2, ..., objN]);
console.log(msg [, subst1, ..., substN]);

Parameters

obj1 ... objN

A list of JavaScript objects to output. The string representations of each of these objects are appended together in the order listed and output. Please be warned that if you log objects in the latest versions of Chrome and Firefox what you get logged on the console is a reference to the object, which is not necessarily the 'value' of the object at the moment in time you call console.log(), but it is the value of the object at the moment you open the console.

msg

A JavaScript string containing zero or more substitution strings.

subst1 ... substN

JavaScript objects with which to replace substitution strings within msg. This gives you additional control over the format of the output.

See Outputting text to the console in the documentation of console for details.

Difference between log() and dir()

You might ask yourself what's the difference between console.dir() and console.log().

Another useful difference in Chrome exists when sending DOM elements to the console.

Notice:

• console.log prints the element in an HTML-like tree
• console.dir prints the element in a JSON-like tree

Specifically, console.log gives special treatment to DOM elements, whereas console.dir does not. This is often useful when trying to see the full representation of the DOM JS object.

There's more information in the Chrome Console API reference about this and other functions.

Logging objects

Don't use console.log(obj), use console.log(JSON.parse(JSON.stringify(obj))).

This way you are sure you are seeing the value of obj at the moment you log it. Otherwise, many browsers provide a live view that constantly updates as values change. This may not be what you want.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Opera Dragonfly documentation: Console
• MSDN: Using the F12 Tools Console to View Errors and Status
• Firebug wiki: Console API - Firebug supports additional features in its console.log() implementation, such as styled logging.
• NodeJS: Console API