Resin 1.1
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Functions
Function Declaration
function [name] (arg_1, ..., arg_n) { statement_list }
The function declaration creates a new function with formal arguments arg_1 through arg_n and body statement_list. If name is given, the function is stored as the value of the variable name. Function declarations are expressions, so they can be used as arguments for functions like sort and replace.
Sort with comparison function
a = [{a:19}, {a:1}, {a:13}] a = a.sort(function(a, b) { return a.a < b.a ? -1 : 1 }) a.toSource()
[{a:1}, {a:13}, {a:19}]
Regexp replace with replace function
"abcdefa".replace(/[ac]/g, function(a) { return a.charCodeAt(0) })
97b99def97
Argument Binding
A function call binds the actual arguments supplied to the call to the formal arguments in the function definition. If the caller supplies fewer arguments than the definition asks for, Resin will bind the value `undefined`. The arguments are treated as local variables, i.e. modifying the arguments will not change any global value. (See the var statement.)
Argument Binding
function foo(a, b) { return a + ' ' + b; } foo(3)
3 undefined
Arguments are locals
var a = "global" function foo(a) { var c = a; a = "local"; return c + ' ' + a; } foo("dummy") + ' ' + a
dummy local global
The `arguments` variable
Function calls also set the `arguments` variable. This array contains the calling arguments in call order. The `arguments` variable allows variable length function calls.
Variable length arguments
function sum() { var sum = 0; for (var i = 0; i < arguments.length; i++) sum += arguments[i]; return sum; } sum(1, 2, 3, 4, 5)
15
The `arguments` variable also contains an alias to each of the formal variables. So `arguments[arg_1]` returns the same value as arg_1. Finally, `arguments` contains the property `callee` which contains the function itself, allowing anonymous functions to make recursive calls.
Anonymous Fibonacci
fib = function (a) { if (a < 2) return 1; else return arguments.callee(a - 1) + arguments.callee(a - 2); } for (var i = 1; i <= 5; i++) writeln(fib(i))
1 2 3 5 8
`this`
The special variable `this` allows functions to access properties of the called object, i.e. it allows them to act as methods instead of free functions. Since JavaScript functions are objects and can be assigned dynamically, the value of `this` depends on how the function is called. If it's called as a method, `this` is the object. If it's called as a free function, `this` is the global object.
call expression | value of `this`
--- | ---
foo() | the global object
obj.foo() | obj
obj["foo"]() | obj
(expr)() | the global object
new foo() | a new object with prototype `foo.prototype`
foo.call(obj) | obj
foo.apply(obj) | obj
Using `this` as class method
class Counter { /** * Return new value of count */ function next() { return this.count++; } /** * Create a new counter */ function Counter(a) { this.count = a; } } counter = new Counter(10); for (var i = 0; i < 3; i++) writeln(counter.next())
10 11 12
Closures | JavaScript 1.2
Scripts can declare functions inside of functions, creating closures. The inner function, i.e. the closure, can access the outer function's local variables as its own variables. In fact, the closure can access the outer function's variables even when the outer function has completed.
Closure
function outer(a) { return function() { return a++ } // incrementing function } next = outer(10); // 'next' can still access 'a' for (var i = 0; i < 3; i++) writeln(next());
10 11 12
Objects |  | Statements
Copyright © 1998-2000 Caucho Technology. All rights reserved. Last modified: Thu, 16 Sep 1999 14:56:48 -0700 (PDT)