Function Properties and Methods
We’ve
seen that functions can be used as data values in JavaScript programs
and that they can be created with the Function( )
constructor. These are sure signs that functions are actually
represented by a type of JavaScript object, the Function object.
Since functions are objects, they have properties and methods, just
like the String and Date objects, for example. Now that we’ve
discussed the call and Arguments objects that are used in the context
of function invocation, let’s turn to the Function object
itself.
The length Property
As we’ve seen, within the body of
a function, the length property of the
arguments array specifies the number of arguments
that were passed to the function. The length
property of a function itself, however, has a different meaning. This
read-only property returns the number of arguments that the function
expects to be passed -- that is, the number
of parameters it declares in its parameter list. Recall that a
function can be invoked with any number of arguments, which it can
retrieve through the arguments array, regardless
of the number of parameters it declares. The
length property of the Function object specifies
exactly how many declared parameters a function has. Note that unlike
arguments.length, this length
property is available both inside and outside of the function body.
The following code defines a function named check( )
that is passed the
arguments array from another function. It compares
the arguments.length ...
Get JavaScript: The Definitive Guide, Fourth Edition now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
