JavaScript Miscellany - Advance Java Web Technology - Lecture Slides, Slides of Computer Science

Download JavaScript Miscellany - Advance Java Web Technology - Lecture Slides and more Slides Computer Science in PDF only on Docsity!

JavaScript Miscellany

Properties of functions

• Functions are objects, and have properties
  • length – the number of formal parameters
  • arguments – the Arguments object, which is “like” an array of actual parameters - Note: length is not necessarily equal to arguments.length
  • caller – the function that invoked this one, or null if the function was invoked from the top level
  • prototype (for constructor functions) – an object that defines properties and methods of functions created with this constructor

Global and local variables

• A variable is local to a function if
  • It is a formal parameter of the function
  • It is declared with var inside the function (e.g. var x = 5 )
• Otherwise, variables are global
• Specifically, a variable is global if
  • It is declared outside any function (with or without var)
  • It is declared by assignment inside a function (e.g. x = 5 )

Methods I

• First we construct an object:
  • function Point(xcoord, ycoord) { this.x = xcoord; // keyword "this" is mandatory this.y = ycoord; }
  • myPoint = new Point(3, 5);
• A method is a function that is associated with, and

invoked through, an object (hence can use this)

• Here is a “function” that makes no sense by itself:
  • function distance(x2, y2) { function sqr(x) { return x * x; } return Math.sqrt(sqr(this.x – x2) + sqr(this.y – y2)); }

The End