node/doc/api/console.markdown

console

Stability: 4 - API Frozen

• {Object}

For printing to stdout and stderr. Similar to the console object functions provided by most web browsers, here the output is sent to stdout or stderr.

The console functions are synchronous when the destination is a terminal or a file (to avoid lost messages in case of premature exit) and asynchronous when it's a pipe (to avoid blocking for long periods of time).

That is, in the following example, stdout is non-blocking while stderr is blocking:

$ node script.js 2> error.log | tee info.log

In daily use, the blocking/non-blocking dichotomy is not something you should worry about unless you log huge amounts of data.

console.log([data], [...])

Prints to stdout with newline. This function can take multiple arguments in a printf()-like way. Example:

console.log('count: %d', count);

If formatting elements are not found in the first string then util.inspect is used on each argument. See util.format() for more information.

console.info([data], [...])

Same as console.log.

console.error([data], [...])

Same as console.log but prints to stderr.

console.warn([data], [...])

Same as console.error.

console.dir(obj)

Uses util.inspect on obj and prints resulting string to stdout.

console.time(label)

Mark a time.

console.timeEnd(label)

Finish timer, record output. Example:

console.time('100-elements');
for (var i = 0; i < 100; i++) {
  ;
}
console.timeEnd('100-elements');

console.trace(label)

Print a stack trace to stderr of the current position.

console.assert(value, [message], [...])

Similar to assert.ok(), but the error message is formatted as util.format(message...).