Javascript1
General Information
This course is currently running November-December 2013, Tuesdays 11:30-1:30.
Instructor: Dan Bauer (email: dsbauer at gmail)
Course Outline
Session 1
- Firebug Console/Interpreter
- Expressions
- An expression (EXPR) can be:
- a primitive (e.g. 1)
- a variable (e.g. x)
- an operator combining smaller EXPR's (e.g. x+1, 2*(x+1))
- An expression (EXPR) can be:
- Operators have:
- keyword or symbol (OP)
- syntax template (e.g. _ OP _)
- unary prefix: OP_
- unary postfix: _OP
- binary infix: _OP_
- ternary infix: _OP_OP_
- one or more inputs _ ("operands")
- one output ("return value")
- may be undefined
- possible side-effects (e.g. change in variable's value)
- Variables have:
- a name/identifier
- a value (initially undefined)
- each value has a type (primitive or reference)
- a scope
- Other (non-expression) Statements
- var NAME;
- var NAME = EXPR;
- if (EXPR) {EXPR;}
- if (EXPR) {EXPR;} else {EXPR;}
- Primitive Types
- undefined
- Number
- same type for integers and floats (fractional)
- special values: NaN ("not a number"), Infinity
- String
- wrapped in either " " or ' '
- may contain opposite quote or other special characters
- \t (tab)
- \n (newline)
- Boolean (true/false)
- false-ish values: false,undefined,null,0,"",NaN
- (some) true-ish values: true,1,"false","undefined","0",{} (empty object)
Some Sample Operators:
| operator | input type | example | result | result type | side effects |
|---|---|---|---|---|---|
| typeof | NUM | typeof 1 | "number" | STR | |
| STR | typeof "word" | "string" | |||
| BOOL | typeof true | "boolean" | |||
| ,
(sequence) |
any | "a", "b", "c" | "c" | type of
last value | |
| (4,"3"),("two",1) | 1 | ||||
| +
(plus) |
NUM | 1+1 | 2 | NUM | |
| +
(concatenate) |
STR | "1"+"1" | "11" | STR | |
| mixed | 1+"2" | "12" | STR | ||
| - * / % | NUM | 3-1 | 2 | NUM | |
| STR | "3"-"1" | 2 | |||
| mixed | "3"-1 | 2 | |||
| < > <= >=
(comparison) |
NUM | 1<2 | true | BOOL | |
| STR | "b"<"a" | false | |||
| ==
(equality) |
NUM | 1==2 | false | BOOL | |
| STR | "a"=="aa" | false | |||
| mixed | 1=="1" | true | |||
| mixed | 0==false | true | |||
| ===
(identity) |
NUM | 1===2 | false | BOOL | |
| STR | "abc"==="abc" | true | |||
| mixed | 1==="1" | false | |||
| mixed | 1===true | false | |||
| !
(not) |
any | !1 | false | BOOL | |
| !"" | true | ||||
| &&
(and) |
any | null && "red" | null | first false-ish
or last input | |
| 1 && "green" | "green" | ||||
| ||
(or) |
any | "yes" || null | "yes" | first true-ish
or last input | |
| "" || 0 | 0 | ||||
| ?:
(conditional) |
any | true? "yes": "no" | "yes" | any | |
| variable assignment operators | x is now... | ||||
| =
(assignment) |
any | x=1 | 1 | same as input | 1 |
| x = "blue" | "blue" | "blue" | |||
| +=
(incremental assignment) |
NUM | x=0; x+=2; | 2 | NUM | 2 |
| STR | x="he"; x+="llo"; | "hello" | STR | "hello" | |
| mixed | x=""; x+=2; | "2" | STR | "2" | |
| ++
(post-increment) |
NUM | x=0; x++; | 0 | NUM | 1 |
| STR | x=""; x++; | 0 | 1 | ||
| ++
(pre-increment) |
NUM | x=0; ++x; | 1 | NUM | 1 |
| STR | x=""; ++x; | 1 | 1 | ||
Session 2
Exercises
- Write a function to calculate, for a group of N people where everyone shakes the hand of everyone else, how many total handshakes there are.
- Write another function to enumerate these interactions, returning a single string describing them all. People may be identified by number. For example, for N=3, it might return:
"#1 meets #2. #1 meets #3. #2 meets #3." (Hint: you may want a second "helper" function to handle a single interaction.)
- Write a function to decide whether a given integer is prime. You may need some of these functions/operators:
- function Math.floor(N): truncates any fractional part of a number N (i.e. returns greatest int <=N)
- function Number.isInteger(N): returns true is N is an integer
- modulo operator %: x%y returns 0 if x divides evenly by y