3.1 Scripting Syntax

This chapter will give you an overview about the syntax used in Silverjuke scripts. If you are already familiar with this, the next chapters describe the objects and methods specific to Silverjuke.

Overview

The syntax for Silverjuke scripts follow the rules defined by ECMAScript, 3rd edition. The syntax is very close to JavaScript, C/C++ and to other well-known languages.

If you have ever written a little program or a script in another language, you should have no problems with Silverjuke scripts.

Variables

Variables have no type attached, and any value can be stored in any variable.

Variables can be declared with a var statement. If this is done, these variables are local to the scope the variable is declared.
Variables declared outside any function, and variables not declared with var, are global and can be used by the entire script.
Variable names (as well as functions and reserved words) are case sensitive.

a = 1;         // declare a global variable
function var_test()
{
  var b = 2;   // this is a variable local to var_test()
  c = 'str';   // this also declares a global variable
}

var_test();    // call var_test()
print(a);      // will print 1
print(b);      // b is undefined as local to var_test()
print(c);      // will print 'str'

Basic Data Types

Basic data types are boolean, numbers, strings, arrays and objects. Conversion between these types is done as needed.

Booleans are values which represent one of the states true or false. Each other data type may be converted to a boolean; this is needed if they are used eg. as expressions in control structures.
Numbers are represented as floating point values. Basic calculations can be done directly using eg. the +, -, *, /, %, ++, –, &, |, ^, << or >> operators, for some advanced calculations, please have a look at the Math Object.
Strings are a sequence of characters and can be created directly by placing the series of characters between double or single quotes. Individual characters within a string can be accessed through the [] operator; to append two strings together, use the + operator. For some advanced operations, please have a look at the String Object.
Arrays are maps from integer numbers to other basic data types. Individual values within an array can be accessed through the [] operator. For some advanced operations, please have a look at the Array Object.
Objects are values with some attached named properties and are usually created using the new operator; some of the named properties may be functions (callable properties). To access properties of an object, use the . operator

a = true;              // create a boolean

b = 12.2;              // assign a number to b
c = 'test string';     // assign a string to c
d = "another string";  // assign a string to d

e = [0,1,2];           // create an array with three elements
f = new Array(0,1,2);  // same using the new operator

g = new Object;        // create a new (empty) object
g.prop = 23;           // assign a property to the object

h = new Date;          // create an object of a predefined class
h.getDay()             // call a method (a callable property) of the object

There is no need to worry about deleting variables - this is done automatically by Silverjuke's garbage collection.

Control Structures

You can use the control structures if, switch, for, while and do..while.

if ( expr ) { statements; } else { statements; }

The curly braces are needed only if you use more than one statment. In general, they are recommended in most cases. The else part is optional.
switch ( expr ) { case 1: statements; break; case 2: statements; break; default: statements; break; }

The curly braces are required, break is optional but recommended in most cases - if left out, execution will continue to the body of the next case block. The default part is optional.
for ( initial-expr; cond-expr; expr evaluated after each loop ) { statements to execute each loop; }

Every expression can be left out if unneeded. The curly braces are needed only if you use more than one statment. In general, they are recommended in most cases.
while ( cond-expr ) { statements; }

The curly braces are needed only if you use more than one statment. In general, they are recommended in most cases.
do { statements; } while ( cond-expr );

The curly braces are needed only if you use more than one statment. In general, they are recommended in most cases. In contrast to while(..){..}, the do{..}while(..) loop is always executed at least one time.

if( program.kioskMode ) {
  // we're in kiosk mode, do what to do
} else  {
  // we're not in kiosk mode, do what to do
}

switch( program.viewMode ) {
  case 0: // we're in album mode, do what to do
    break;

  case 1: // we're in cover mode, do what to do
    break;

  default: // handle other modes here
    break;
}

Functions

A function is a block with a (possibly empty) argument list and an optional name. A function may give back a return value.

// declare the function
function my_func_text( a )
{
  print( a ); // call the predefined function print()
}

// call the function
my_func_test( 'Hello!' );

// functions may also be used as properties for objects:
program.launchBrowser( 'http://...' );

// you can also give "anonymous" (unnamed) functions directly as arguments:
program.addMenuEntry( 'bla', function(){alert('Unamed function')} );

Are arguments given by value or by reference? This is quite easy to answer:

Booleans, Numbers and Strings are given by value - you get a copy of the value, if you change the value, the changes are not visible to the caller.
All other types are given by reference for performance reasons - if you change eg. an object given as an argument, these changes are visible to the caller.

Error Handling

If any error occur while your script is executed, an error object is thrown. You may catch these errors using a try..catch block:

try {
  // do what to do here
}
catch(err) {
  // if any error occurs in the try block above, we go here.
}
// here we go if no erros occur

If any error is thrown outside a try..catch block, the script is terminated immediately; in this case - and eg. for syntax errors - Silverjuke logs and error to the console window.

BTW: You can also easily test a function, a macro or a little script by just entering it to the text file and click on "Evaluate".

Now, as you have an idea about the syntax, you may want to have a look at the next chapters which describe the objects and methods specific for Silverjue.

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