Transcript Diapositiva 1

JavaScript: An Analysis
Michael Owen
Brief History
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Founded at NetScape by Brendan Eich
Mocha, LiveScript, then JavaScript
No apparent relation to Java
Embedded in HTML
Interpreted language
Microsoft’s version is Jscript
Standardized in Nov. 1996
Data Types
• Only three primitive types
– String
– Number
– Boolean
• All numbers are stored as floating point
numbers
• Variables are not explicitly declared
Object-Oriented Support
• Prototype-oriented programming
• Everything but primitive types are
considered objects
• Objects seem hidden within the code
• Arrays are dynamic which can be
dangerous
• Fully supports inheritance, encapsulation,
and polymorphism
Subprograms
• Functions are treated as objects but act
the same way you’d expect
• Parameters are more like guidelines
• Can call functions recursively
• Can declare functions within functions
Readability of JavaScript
• Easy to read if familiar with Java or C++
• Suffers a bit since variables are never
declared with a type
• Orthogonality is high with only three
primitive data types
• Can perform any operation between any
two data types
Writability of JavaScript
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Only a few data types to learn
Don’t need to worry about declarations
No type checking
Objects are a little convoluted
Easy to write, but at what cost?
Reliability of JavaScript
• Suffers due to lack of type checking
• Really depends on what purpose the code
is for
• Better used for less important tasks
Cost of JavaScript
• Very small if the team is already familiar
with Java or C++
• Does not need to compile
• Does not require a lot of system resources
Bottom Line
• Overall, a very good language
• Does a lot of things right
• Does one thing very wrong