Javascript console.log(object) vs. concatenating string

The + x coerces the object x into a string, which is just [object Object]:

http://jsfiddle.net/Ze32g/

The pretty printing is a very nice and probably very complex underlying code that someone implemented as part of the console object and the log method.

Try this:

console.log("hmm: ", x);

The console.log function

'console.log' is an overloaded function that accepts a list of parameters that are either passed by copy (string|number|boolean) or by reference (everything else).

In the case of values passed by copy, the value is printed by casting it as a string.
In the case of values passed by reference, the value is pretty printed as the browser sees fit.

The + operator

The plus sign operator (+) is overloaded. When both sides of the operator are numbers, the sum of the two operators is returned.

If either side of the operator is a string, then both sides will be cast as string and the concatenation of those two strings will be returned.

console.log("hmm: " + x);

is the same as writing

console.log(String("hmm: ") + String(x));

Solution

Prevent the implicit string casting by swapping the plus sign (+) with a comma (,)

console.log("hmm: ", x);

More Info

For a more in depth description of the 'console.log' function, see:
https://developer.mozilla.org/en-US/docs/DOM/console.log

For a more in depth description on the plus sign operator (+), see:
http://www.w3schools.com/js/js_operators.asp

Use JSON.stringify when printing an object with string appending

console.log("Haa"+JSON.stringify(x))