Mastering JavaScript

Functions, Closures, and Modules
return 'trueMoo';
};
}
else {
sayMoo = function() {
return 'falseMoo';
};
}
foo();
If you are curious to know why you should not use function declarations in
conditional blocks, read on; otherwise, you can skip the following paragraph.
Function declarations are allowed to appear only in the program or function body.
They cannot appear in a block ({ ... }). Blocks can only contain statements and
not function declarations. Due to this, almost all implementations of JavaScript have
behavior different from this. It is always advisable to never use function declarations
in a conditional block.
Function expressions, on the other hand, are very popular. A very common pattern
among JavaScript programmers is to fork function definitions based on some kind
of a condition. As such forks usually happen in the same scope, it is almost always
necessary to use function expressions.
The arguments parameter
The arguments parameter is a collection of all the arguments passed to the function.
The collection has a property named length that contains the count of arguments,
and the individual argument values can be obtained using an array indexing
notation. Okay, we lied a bit. The arguments parameter is not a JavaScript array, and
if you try to use array methods on arguments, you'll fail miserably. You can think of
arguments as an array-like structure. This makes it possible to write functions that
take an unspecified number of parameters. The following snippet shows you how
you can pass a variable number of arguments to the function and iterate through
them using an arguments array:
var sum = function () {
var i, total = 0;
for (i = 0; i < arguments.length; i += 1) {
total += arguments[i];
}
return total;
};
console.log(sum(1,2,3,4,5,6,7,8,9)); // prints 45
console.log(sum(1,2,3,4,5)); // prints 15
[ 60 ]
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