Expressions and Statemen

JavaScript 两个最重要的概念表达式和语句

表达式概念：An expression is a phrase of JavaScript that a JavaScript interpreter can evaluate to produce a a value.

表达式的分类:

1.Primary Expressions

 1 "hi word"
 2 /pattern/
 3 
 4 //some of JavaScript reserved word are primary expressions
 5 true
 6 false
 7 null
 8 this //Evaluates to the "current" object
 9 
10 //finally the third type of primary expressions is the bare variable reference
11 I
12 sum
13 undefined // undefined is a global variable ,not like null.

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2.Object and Array Initalizers

1 // Array initializer
2  [1,5,2,6,5]
3 
4 // Object initializer
5 {x:2,y3}

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3. Function Definition Expressions

1 //*function expression
2 function(x) { return x*x }
3 
4 //* function statement 
5 function foo(){
6  console.log("bar");
7 };

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4.Property Access expression & Invoication expression & Object Creation expression

 1 //Property Access expression
 2 var o={x:1,y:{z:3}}
 3 var a=[o,1,4,[5,6]]
 4 
 5 o.x //property x of expression o
 6 o["y"] //property x of expression o
 7 a[1] //element at index 1 of object o
 8 a[0].x // property x of expression a[0]
 9 
10 //Invocation expression
11 foo(1,2)
12 a.sort()
13 Math.max(x,y,z)
14 
15 //object creation expression
16 new Object()
17 new Point(2,3)

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5.Arithmetic Expression & Logical Expression & Assignment Expression

 1 //Arithmetic 
 2 1+1
 3 2*5
 4 3-4
 5 6%9
 6 5--
 7 6++
 8 
 9 //Logical
10 7&8
11 7<<2
12 ^0x0f
13 // Assignment
14 I=6
15 o.x=2
16 
17 x +=x+1
18 .......

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语句概念：statements are JavaScript sentences or commands；Expressions are evaluated to produce a value, but statements are
executed to make something happen.

语句的分类:

Statement	Syntax	Purpose
break	break [label];	Exit from the   innermost loop or switch or from named enclosing statement
case	case expression:	Label a statement   within a switch
continue	continue   [label];	Begin next iteration   of the innermost loop or the named loop
debugger	debugger;	Debugger breakpoint
default	default:	Label the default   statement within a switch
do/while	do statement while   (expression);	An alternative to the   while loop
empty ;	Do nothing
for	for(init; test; incr)   statement	An easy-to-use loop
for/in   for	(var in object)   statement	Enumerate the   properties of object
function	function   name([param[,...]]) { body }	Declare a function   named name
if/else	if (expr) statement1   [else statement2]	Execute statement1 or   statement2
label	label: statement	Give statement the   name label
return	return   [expression];	Return a value from a   function
switch	switch (expression) {   statements }	Multiway branch to   case or default: labels
throw	throw   expression;	Throw an exception
try	try { statements   }	Handle exceptions
	[catch { handler   statements }]
	[finally{ cleanup   statements }]
use   strict	use strict;	Apply strict mode   restrictions to script or function
var	var name [ = expr] [   ,... ];	Declare and   initialize one or more variables
while	while (expression)   statement	A basic loop   construct
with	with (object)   statement	Extend the scope   chain (forbidden in strict mode)