Why does this work (returns "one, two, three"):
var words = ['one', 'two', 'three']; $("#main").append('<p>' + words.join(", ") + '</p>');
and this work (returns "the list: 111"):
var displayIt = function() { return 'the list: ' + arguments[0]; } $("#main").append('<p>' + displayIt('111', '222', '333') + '</p>');
but not this (returns blank):
var displayIt = function() { return 'the list: ' + arguments.join(","); } $("#main").append('<p>' + displayIt('111', '222', '333') + '</p>');
What do I have to do to my "arguments" variable to be to use .join() on it?
Function arguments are the real values passed to (and received by) the function.
You can access specific arguments by calling their index. var add = function (num1, num2) { // returns the value of `num1` console. log(arguments[0]); // returns the value of `num2` console.
In mathematics, an argument of a function is a value provided to obtain the function's result. It is also called an independent variable. For example, the binary function has two arguments, and , in an ordered pair . The hypergeometric function is an example of a four-argument function.
The apply() method calls the specified function with a given this value, and arguments provided as an array (or an array-like object).
It doesn't work because the arguments
object is not an array, although it looks like it. It has no join
method:
>>> var d = function() { return '[' + arguments.join(",") + ']'; } >>> d("a", "b", "c") TypeError: arguments.join is not a function
To convert arguments
to an array, you can do:
var args = Array.prototype.slice.call(arguments);
Now join
will work:
>>> var d = function() { var args = Array.prototype.slice.call(arguments); return '[' + args.join(",") + ']'; } >>> d("a", "b", "c"); "[a,b,c]"
Alternatively, you can use jQuery's makeArray
, which will try to turn "almost-arrays" like arguments
into arrays:
var args = $.makeArray(arguments);
Here's what the Mozilla reference (my favorite resource for this sort of thing) has to say about it:
The
arguments
object is not an array. It is similar to an array, but does not have any array properties exceptlength
. For example, it does not have the pop method. ...The
arguments
object is available only within a function body. Attempting to access the arguments object outside a function declaration results in an error.
If you are not interested on other Array.prototype
methods, and you want simply to use join
, you can invoke it directly, without converting it to an array:
var displayIt = function() { return 'the list: ' + Array.prototype.join.call(arguments, ','); };
Also you might find useful to know that the comma is the default separator, if you don't define a separator, by spec the comma will be used.
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