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. View Code

2.Object and Array Initalizers

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

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 }; View Code

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) View Code

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 ....... View Code

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 Purposebreak break [label]; Exit from the   innermost loop or switch or from named enclosing statementcase case expression: Label a statement   within a switchcontinue continue   [label]; Begin next iteration   of the innermost loop or the named loopdebugger debugger; Debugger breakpointdefault default: Label the default   statement within a switchdo/while do statement while   (expression); An alternative to the   while loopempty ; Do nothing　for for(init; test; incr)   statement An easy-to-use loopfor/in   for (var in object)   statement Enumerate the   properties of objectfunction function   name([param[,...]]) { body } Declare a function   named nameif/else if (expr) statement1   [else statement2] Execute statement1 or   statement2label label: statement Give statement the   name labelreturn return   [expression]; Return a value from a   functionswitch switch (expression) {   statements } Multiway branch to   case or default: labelsthrow throw   expression; Throw an exceptiontry try { statements   } Handle exceptions　[catch { handler   statements }]　　[finally{ cleanup   statements }]　　　　use   strict use strict; Apply strict mode   restrictions to script or functionvar var name [ = expr] [   ,... ]; Declare and   initialize one or more variableswhile while (expression)   statement A basic loop   constructwith with (object)   statement Extend the scope   chain (forbidden in strict mode)