DePaul IT 130 - JavaScript 2 (29 pages)

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JavaScript 2



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JavaScript 2

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Pages:
29
School:
DePaul University
Course:
It 130 - Introductory Computing for the Web
Unformatted text preview:

Javascript II Expressions and Data Types JavaScript Review programs executed by the web browser programs embedded in a web page using the script element programs consist of statements executed sequentially 2 Statements End with semi colon Cannot occupy multiple lines Assignment statement var value The value on the right can be any legal expression Function call document write foo 3 Variables A variable is a named location where a value can be stored In JavaScript Other languages using a variable creates it can also declare require that variables be declared before being used Variables have scope locations in the program where they are valid will discuss this later on 4 Variable declaration Declaration is optional in Javascript Syntax var foo Says that foo is a variable we will use later 5 Data types What is the difference between the following statements val1 53 val2 53 These values are different to JavaScript stored differently manipulated differently same operation may mean something different on strings in concatenation on numbers is addition 6 Data Type A characterization of a stored value Determines what kinds of values can be stored how the value is stored internally what operations can be applied Syntactic representation how the value is expressed in a program 7 JavaScript Types Strings Integers Floats real numbers Boolean true or false 8 Strings What values What operations lists of characters any length including the zero length null string concatenation operator output to the Web page using document write returned by prompt function Syntax double or single quotes 9 Examples val1 Hello val2 there val3 val1 val2 document write val3 val4 45 val2 val3 val5 document write val2 10 Integers What values What operations standard mathematical operations special math functions Syntax whole numbers between 9223372036854775808 and 9223372036854775808 unquoted integers Note book doesn t use integers in examples 11 Examples val1 45 val2 055 val3 val1 val2 Math sqrt val3 12 Float What values What operations decimal values from 1 0x10308 to 1 0x10 323 17 digits of precision past decimal point standard mathematical operations special math functions Syntax unquoted decimal values scientific notation 1 2e3 1 2 x 103 1200 13 Examples val1 5 3 val2 5 3e1 val3 val1 val2 Math floor val3 14 Boolean What true false What values operations logical operations and or not Syntax keywords true false 15 Examples val1 true val2 false val3 val1 val2 16 Another kind of value script type text javascript var foo document write foo script What is the value of foo 17 undefined value This is the value of a variable when it is created if you use a variable without defining it you get an error You can declare a variable without giving it a value not an error variable has no value unexpected results 18 Expressions An expression is a legal combination of Javascript values operators function calls and variables that evaluates to a value Examples a b 5 6 3 14159 r r Math sqrt errorTerm foo bar 19 Syntax alert An expression is not a statement an expression may be part of a statement note no semi colon Example a b 2 expression size a b statement 20 Evaluation An expression is evaluated when it is executed run time Steps Each variable is replaced by its current value Operators are applied Until a single value remains 21 Example a 5 b 20 position a 5 b 10 22 Complex expression Expressions can be large and complex JavaScript doesn t care Readers of your program might care A complex expression can always be simplified by using intermediate variables 23 Example complex expression slope y1 y2 x1 x2 simplified deltaY y1 y2 deltaX x1 x2 slope deltaY deltaX 24 The trap means different things for different types foo bar foobar 5 6 56 5 6 11 What about 5 6 6 foo 25 Operators is an operator An operator takes two values sometimes one makes returns a new value Some operators are two characters Assignment is not an operation is not an operator 26 Functions Like an operator takes values does some operation returns a result But has a name instead of symbol can take any number of values can be user defined 27 Predefined Functions You can define your own functions later in the class Many built in prompt document write 28 Function syntax prompt Enter a number 0 function name parameter 1 parameter 2 parameter list return value is a string containing the user input No parameters Math random there s still a list just an empty one 29


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