Javascript1

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))

• Operators have:
  • keyword or symbol (OP)
  • syntax template (e.g. _ OP _)
    • prefix: OP_
    • postfix: _OP
    • infix: _OP_
    • compound: _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
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