JavaScript for ABAP Programmers - 2/7 Data Types

JavaScript for ABAP Programmers
Data Types
Chris Whealy / The RIG

ABAP
Strongly typed
Syntax similar to COBOL
Block Scope
No equivalent concept
OO using class based inheritance
Imperative programming

JavaScript
Weakly typed
Syntax derived from Java
Lexical Scope
Functions are 1st class citizens
OO using referential inheritance
Imperative or Functional programming

Strongly Typed vs. Weakly Typed Languages
There are two schools of thought for determining how data should be stored in variables:
• ABAP uses Strong (or Static) Typing
Apart from field symbols, all ABAP variables
must have their data type defined at declaration
time

© 2013 SAP AG. All rights reserved.

3

• JavaScript uses Weak (or Dynamic) Typing
A variable takes on the data type of whatever
value it currently holds
time


4

time
• Pros and Cons of Strong Typing

+ Data type errors can be trapped at compile time
- Rigid type systems reduce language flexibility


5

time
• Pros and Cons of Weak Typing


- Data type errors can only be trapped at runtime
+ Highly flexible type system allows for a dynamic
style of coding


6

time
• Pros and Cons of Weak Typing


- Data type errors can only be trapped at runtime
+ Highly flexible type system allows for a dynamic
style of coding

Compiled languages (E.G. ABAP, Java, C) tend to use strong typing, whereas interpreted scripting
languages (E.G. JavaScript, Ruby, Python) tend to use weak typing.


7

JavaScript Data Types: Overview
In JavaScript, there are only 6 data types.
At any one time the value of a variable belongs to one and only one of the following data types.

Data Type

This value of this variable…

Null

Is explicitly defined as having no value

Undefined

Is indeterminate

Boolean

Is either true or false

String

Is an immutable collection of zero or more Unicode characters

Number

Can be used in mathematical operations

Object

Is an unordered collection of name/value pairs


8

JavaScript Data Types 1/3
In the coding, the data types are specified as follows:
// -----------------------------------------------------------------------------------------------// Special
null;
// Indicates an explicit non-value
undefined;
// Indicates an indeterminate value (E.G. a variable is declared but not initialised)


9

// -----------------------------------------------------------------------------------------------// Special
null;
undefined;
// -----------------------------------------------------------------------------------------------// Boolean
true;
false;


10

// -----------------------------------------------------------------------------------------------// Special
null;
undefined;
// -----------------------------------------------------------------------------------------------// Boolean
true;
false;
// -----------------------------------------------------------------------------------------------// String – contains zero or more Unicode characters
'Bazinga!';
// Can be delimited by either single quotes
"";
// Or double quotes


11

// -----------------------------------------------------------------------------------------------// Number
3.1415926;
// Stored as 64-bit floating point number
1;
// Be careful, this is stored as floating point value, not an integer!


12

// -----------------------------------------------------------------------------------------------// Number
3.1415926;
1;
// Warning! All the usual problems associated with trying to represent decimal values in binary
// floating point format still apply in JavaScript!
var result = 0.1 + 0.2;
result;
//  0.30000000000000004, not 0.3 (Decimal 0.1 has no exact binary equivalent)


13

// -----------------------------------------------------------------------------------------------// Number
3.1415926;
1;
// Warning! All the usual problems associated with trying to represent decimal values in binary
// floating point format still apply in JavaScript!
var result = 0.1 + 0.2;
result;
//  0.30000000000000004, not 0.3 (Decimal 0.1 has no exact binary equivalent)
// Special numerical values that could be returned in the event of illegal mathematical operations
// (These values are actually stored as properties of the Global Object)
NaN;
// 'Not a Number' E.G. 1/'cat'  NaN
Infinity;
// The result of division by zero


14

In addition to the basic data type of Object, JavaScript provides several built-in objects that behave as
if they were composite data types. E.G. Array, Date, Function, Math and RegEx etc.
// -----------------------------------------------------------------------------------------------// Object. Zero or more unordered name:value pairs of any data type delimited by curly braces
{ pet1: 'cat',
pet2: 'dog' };


15

{ pet1: 'cat',
pet2: 'dog' };
// Array object. Zero or more values of any data type accessed by a numerical, 0 based index
[1,2,3,4,5];


16

{ pet1: 'cat',
pet2: 'dog' };
[1,2,3,4,5];
// Function object. A special object that has both properties and executable content
function() { /* statements */ }


17

{ pet1: 'cat',
pet2: 'dog' };
[1,2,3,4,5];
// Math object. Contains many useful mathematical functions and constants
Math.PI; //  3.141592653589793


18

{ pet1: 'cat',
pet2: 'dog' };
[1,2,3,4,5];
Math.PI; //  3.141592653589793
// Regular Expression Object. A tool for specifying and extracting patterns of text within a string
/^(?:([A-Za-z]+):)?(/{0,3})([0-9.-A-Za-z]+)(?::(d+))?(?:/([^?#]*))?(?:?([^#]*))?(?:#(.*))?$/;


19

{ pet1: 'cat',
pet2: 'dog' };
[1,2,3,4,5];
Math.PI; //  3.141592653589793
// Regular Expression Object. A tool for specifying and extracting patterns of text within a string
// Regular expressions are sometimes confused with Egyptian hieroglyphics... :-)


20

Variables and Data Types
In weakly typed languages such as JavaScript, there is no concept of declaring that a variable should hold data of
a particular type. The data type of a variable is determined simply by the value it currently holds.
// A weakly typed language means that data types are determined
// dynamically at runtime, not statically at design time
var whoAmI = 'Hello world';


// Variable 'whoAmI' is both declared & assigned a string value

21



whoAmI = 1.61792;
whoAmI = [1,2,3,4,5];

// Now it's a number
// Now it's an array


22



whoAmI = 1.61792;
whoAmI = [1,2,3,4,5];


whoAmI = true;

// Now it's a Boolean


23



whoAmI = 1.61792;
whoAmI = [1,2,3,4,5];


whoAmI = true;


whoAmI = {
// Now it's an object
someProperty: 'Hello world'
}


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whoAmI = 1.61792;
whoAmI = [1,2,3,4,5];


whoAmI = true;


whoAmI = {
// Now it's an object
someProperty: 'Hello world'
}
whoAmI = function() { };


// Now it's a...you get the idea

25

JavaScript for ABAP Programmers - 2/7 Data Types

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