Expressions and Statemen

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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 reference11 I12 sum13 undefined // undefined is a global variable ,not like null.

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2.Object and Array Initalizers

1 // Array initializer2  [1,5,2,6,5]3 4 // Object initializer5 {x:2,y3}

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3. Function Definition Expressions

1 //*function expression2 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 expression11 foo(1,2)12 a.sort()13 Math.max(x,y,z)14 15 //object creation expression16 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 //Logical10 7&811 7<<212 ^0x0f13 // Assignment14 I=615 o.x=216 17 x +=x+118 .......

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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 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)　　　

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