Function

Overview

JavaScript functions have key properties like constructor, which specifies the function that creates an object's prototype, and length, which indicates the number of expected arguments. These properties allow developers to inspect and manage function behaviors.

Methods such as apply(), bind(), call(), and toString() provide flexible ways to manipulate function contexts, invoke functions with specific arguments, and retrieve their source code.

Practical examples demonstrate how these features enhance function utility in Servoy applications.

Each function in javascript is actually a Function instance.

For more information see: Function (MDN).

Properties Summarized

Type	Name	Summary
Function	constructor	Specifies the function that creates an object's prototype.
Number	length	Specifies the number of arguments expected by the function.

Methods Summarized

Type	Name	Summary
void	apply()	Applies the method of another object in the context of a different object (the calling object); arguments can be passed as an Array object.
void	bind()	Creates a new function which, when called, itself calls this function in the context of the provided value, with a given sequence of arguments preceding any provided when the new function was called.
void	call()	Calls (executes) a method of another object in the context of a different object (the calling object); arguments can be passed as they are.
String	toString()	Returns a string representing the source code of the function.

Properties Detailed

constructor

Specifies the function that creates an object's prototype.

Type Function

Sample

function Tree(name) {
	this.name = name;
}
theTree = new Tree("Redwood");
console.log("theTree.constructor is " + theTree.constructor);

length

Specifies the number of arguments expected by the function.

Type Number

Sample

function addNumbers(x, y){
	if (addNumbers.length == 2) {
		return (x + y);
	} else
		return 0;
}

Methods Detailed

apply()

Applies the method of another object in the context of a different object (the calling object); arguments can be passed as an Array object.

Returns: void

Sample

function book(name, author) {
	this.name = name;
	this.author = author;
}

function book_with_topic(name, author, topic) {
	this.topic = topic;
	book.apply(this, arguments);
}
book_with_topic.prototype = new book();

var aBook = new book_with_topic("name","author","topic");

bind()

Creates a new function which, when called, itself calls this function in the context of the provided value, with a given sequence of arguments preceding any provided when the new function was called.

Returns: void

Sample

var x = 9,
	module = {
		getX: function() {
		     return this.x;
		},
		x: 81
	};
//  "module.getX()" called, "module" is "this", "module.x" is returned
module.getX(); // > 81
//  "getX()" called, "this" is global, "x" is returned
getX(); // > 9
//  store a reference with "module" bound as "this"
var boundGetX = getX.bind(module);
//  "boundGetX()" called, "module" is "this" again, "module.x" is returned
boundGetX(); // > 81

call()

Calls (executes) a method of another object in the context of a different object (the calling object); arguments can be passed as they are.

Returns: void

Sample

function book(name) {
	this.name = name;
}

function book_with_author(name, author) {
	this.author = author;
	book.call(this, name);
}
book_with_author.prototype = new book();

var aBook = new book_with_author("name","author");

toString()

Returns a string representing the source code of the function. Overrides the Object.toString method.

Returns: String

Sample

function printHello() {
	return "Hello";
}
application.output(printHello.toString());

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