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))