Why does arguments in Javascript return [object Arguments] when using console.log?

Question

I have the following function

//simple function with parameters and variable
        function thirdfunction(a,b,c,d){
            console.log("the value of a is: " + a);
            console.log("the value of b is: " + b);
            console.log("the value of c is: " + c);
            console.log("the value of d is: " + d);
            console.log("the arguments for each values are: " + arguments);
            console.log("the number of arguments passed are: " + arguments.length);
        }

        console.log("no parameter values are passed");
        thirdfunction();

        console.log("only a and b parameter values are passed");
        thirdfunction(1,2);

However when the values passed in arguments are not displayed if I concatenate the text the arguments for each values are:. Why is that?

The output I have from Google's console is as follows when concatenating;

no parameter values are passed
the value of a is: undefined
the value of b is: undefined
the value of c is: undefined
the value of d is: undefined
the arguments for each values are: [object Arguments]
the number of arguments passed are: 0
only a and b parameter values are passed
the value of a is: 1
the value of b is: 2
the value of c is: undefined
the value of d is: undefined
the arguments for each values are: [object Arguments]
the number of arguments passed are: 2

The following values are passed when I don't concatenate.

no parameter values are passed
the value of a is: undefined
the value of b is: undefined
the value of c is: undefined
the value of d is: undefined
[]
the number of arguments passed are: 0
only a and b parameter values are passed
the value of a is: 1
the value of b is: 2
the value of c is: undefined
the value of d is: undefined
[1, 2]
the number of arguments passed are: 2

EDIT

Not sure why the question got down voted but the problem I have is that when I use the statement console.log("the arguments for each values are: " + arguments); the output in the console is console.log("the arguments for each values are: " + arguments); however if I pass the statement console.log(arguments); the output in the console is [] or [1, 2]?

I don't fully understand your question. Where is the arguments variable set? Also the arguments passed to the function will default to undefined if not set. — AO_
– AO_, Commented Jun 19, 2012 at 21:46
@hsmoore arguments does not need to be set, it is available in all functions, it is an array representing all arguments called with the function. — Josh Mc
– Josh Mc, Commented Jun 19, 2012 at 21:49
@hsmoore.com - As per my example if I do console.log("the arguments for each values are: " + arguments); the response returned is [object Arguments] whilst if I do ` console.log("the arguments for each values are: " + arguments);` I get [] or [1, 2] — PeanutsMonkey
– PeanutsMonkey, Commented Jun 19, 2012 at 21:50
@PeanutsMonkey - A note here, arguments is not an array, that's why it only shows [object Arguments]. — Derek 朕會功夫
– Derek 朕會功夫, Commented Jun 19, 2012 at 21:52

jsalonen · Accepted Answer · 2012-06-19 21:48:28Z

5

Writing console.log("..." + arguments) it will force conversion of arguments into string. Since arguments is an object, its string representation is [object Arguments]. If you instead want to display contents of that object, try passing it without concatenation:

console.log("the arguments for each values are: ", arguments);

answered Jun 19, 2012 at 21:48

jsalonen

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