I am having a hard time understanding the arguments object. In this code, what function would arguments be looking at?
getAjax('get_info', 'java_array', realVarName, cld.listArray, 0, '',
'no_restrict', function() {
show_list(arguments[0], sld);
if (typeof(postFunc) == "function") {
postFunc();
}
});
'arguments' is an inherit variable with any function. It contains all the parameters passed to a function. For instance, a function definition may not list any parameters, however an invocation could include 'n' parameters on it. The function could then still access all of them through the arguments array.
The arguments object is an Array-like object corresponding to the arguments passed to a function.
In your code the arguments[0] will primarily be undefined
arguments[0] will be undefined or not. It depends entirely upon what getAjax() passed to the callback when it calls it. If it passes arguments, then arguments[0] will certainly have a value.First off, arguments is an object that represents the set of arguments passed to the current function. It exists automatically inside of every function. You can read more about it here on MDN.
So, in your case, arguments[0] will be the first argument that getAjax() passes to the callback you passed into it as the last argument when you called getAjax(). So, it depends upon the internal behavior of getAjax() which you do not show us.
Let's walk through how your code works:
getAjax() and pass it a number of arguments.getAjax() is doing its job, it will, at some point, call that callback function.arguments object will represent whatever arguments were passed to it by getAjax().arguments[0] and pass it to show_list(), you will be passing whatever the first argument was that getAjax() passed to your callback.You could rewrite your code without using the arguments object like this by just declaring a named argument for your callback:
getAjax('get_info', 'java_array', realVarName, cld.listArray, 0, '',
'no_restrict', function(obj) {
show_list(obj, sld);
if (typeof(postFunc) == "function") {
postFunc();
}
});
In this alternate implementation, you name the first argument to the callback function to be obj and use it directly rather than using arugments[0]. Both your implementation and this produce the same result.
It is generally better to use named arguments (like the obj in my alternate implementation) when you know what arguments are going to be passed to a function as this makes the code more self documenting. But the arguments object can be particularly useful when you don't know how many arguments are going to be passed to a function or when you want to pass whatever arguments were passed to your function to some other function (forwarding or proxying).