1. ECMAScript 262-3
@chenchengpro

2. Why ECMAScript?

3. History
• ECMA 262-3 1999 (current)
• ECMA 262-5 2009

4. SPEC ~

5. 1. Scope
2. Conformance
3. References
4. Overview ( )
5. Notational Conventions ( )
6. Source Text ( )
7. Lexical Conventions ( )
8. Types ( )
9. Type Convertion ( )
10. Execution Contexts ( )
11. Expressions ( )
12. Statements ( )
13. Function Definition ( )
14. Program
15. Native ECMAScript Objects (ECMAScript )
16. Errors ( )

6. 1. Scope
2. Conformance
3. References
4. Overview ( )
5. Notational Conventions ( )
6. Source Text ( )
7. Lexical Conventions ( )
8. Types ( )
9. Type Convertion ( )
10. Execution Contexts ( )
11. Expressions ( )
12. Statements ( )
13. Function Definition ( )
14. Program
15. Native ECMAScript Objects (ECMAScript )
16. Errors ( )

7. 1. Scope
2. Conformance
3. References
4. Overview ( )
5. Notational Conventions ( )
6. Source Text ( )
7. Lexical Conventions ( )
8. Types ( )
9. Type Convertion ( )
10. Execution Contexts ( )
11. Expressions ( )
12. Statements ( )
13. Function Definition ( )
14. Program
15. Native ECMAScript Objects (ECMAScript )
16. Errors ( )

8. Structure
Expression, Statement, Function, ...
Type, Type Convention

9. Definitions
• Host Object ( )
• Native Object ( )
• Build-in Object ( )

10. Definitions
• Host Object ( )
• Native Object ( )
• Build-in Object ( )
test XMLHttpRequest, String, var obj = {}

11. Type
• Undefined
• Null
• Boolean (Primitive)
• String
• Number
• Object

12. Object
ReadOnly
DontEnum
DontDelete
Internal

13. [[Prototype]]
[[Class]]
[[Value]]
[[Get]] ( )
[[Put]] ( , )
[[CanPut]] ( )
[[HasProperty]] ( )
[[Delete]] ( )
[[DefaultValue]] (hint) ( )
[[Construct]] caller ( ) new
[[Call]] caller ( )
[[hasInstance]] ( ) ( )
[[Scope]]
[[Match]] (String, Index)

14. Type
• Reference
• List (Internal)
• Completion

15. Reference
•
• base
• propertyName
• delete operator
•
• identifier evaluate
• property accessor

16. Reference
var foo;
function bar() {}
//////////////////////
fooReference = {
base: global,
propertyName: ‘foo’
}
barReference = {
base: global,
propertyName: ‘bar’
}

17. Reference
function foo() {
var bar;
}
//////////////////////
FooBarReference = {
base: foo.__scope__, //
propertyName: ‘bar’
}

18. Reference
var foo = {
bar: ‘’
};
//////////////////////
FooBarReference = {
base: foo,
propertyName: ‘bar’
}

19. Reference
GetBase(V) base
GetPropertyName(V)
Reference V
GetValue(V)
V base
V base
PutValue(V, W)
W

20. Type Convention
• ToPrimitive
• ToBoolean
• ToNumber, ToInteger
• ToString
• ToObject

21. ToPrimitive
ToPrimitive(Value, PreferredType)
Undefined
Null
Boolean
Number
String
Object [[DefaultValue]]
Object
PreferredType

22. [[DefaultValue]]
[[DefaultValue]](hint)
• hint String toString()
valueOf()
• hint Number valueOf(),
toString()
• hint Number
(Date String)

23. ToBoolean
Undefined FALSE
Null FALSE
Boolean
Number +0, -0 NaN false, true
(length 0) false
String
true
Object TRUE

24. ToNumber
Undefined NaN
Null 0
Boolean true 1 false +0
Number
StringNumericLiteral
String
NaN
ToPrimate(V, Number)
Object
ToNumber()

25. ToString
Undefined “undefined”
Null “null”
Boolean “true” “false”
Number ...
String
ToPrimate(V, String)
Object
ToString()

26. ToObject
Undefined TypeError
Null TypeError
Boolean new Boolean()
Number new Number()
String new String()
Object

27. '' == '0' // ?
0 == '' // ?
0 == '0' // ?
false == 'false' // ?
false == '0' // ?
false == undefined // ?
null == undefined // ?
' trn ' == 0 // ?
[] == 0 // ?
var obj = {};
obj.valueOf=function(){return 1};
obj.toString=function(){return 0;}
obj == 1; // ?

28. “equals operator”

29. 11.9.1 The Equals Operator (== )
The production EqualityExpression : EqualityExpression ==
RelationalExpression is evaluated as follows:
1. EqualityExpression
2. GetValue(Result(1))
3. RelationalExpression
4. GetValue(Result(3))
5. Result(4) == Result(2) ( 11.9.3)
6. Result(5).

30. 11.9.3 The Abstract Equality Comparison Algorithm
The comparison x == y, where x and y are values, produces true or
false. Such a comparison is performed as follows:
1. Type(x) Type(y) 14
2. Type(x) Undefined, true
3. Type(x) Null, true
4. Type(x) Number, 11
5. x NaN, false
6. y NaN, false
7. x y , true
Type(x)
8. x +0 y -0, true Number
9. x is -0 y +0, true
10. false

31. 11. Type(x) String,
true false
12. Type(x) Boolean, x y true
false true false Type(x)
13. x y
Number
( 13.1.2) false

32. 14. x null y undefined, true.
15. x undefined y null, true.
16. Type(x) Number Type(y) String, x ==
ToNumber(y)
17. Type(x) String Type(y) Number, ToNumber
(x)== y
18. Type(x) Boolean, ToNumber(x)== y
19. Type(y) Boolean, x == ToNumber(y)
20. Type(x) String Number Type(y) Object,
x == ToPrimitive(y)
21. Type(x) Object Type(y) String Number,
ToPrimitive(x)== y
22. Return false.

33. '' == '0' // ?
0 == '' // ?
0 == '0' // ?
false == 'false' // ?
false == '0' // ?
false == undefined // ?
null == undefined // ?
' trn ' == 0 // ?
[] == 0 // ?
var obj = {};
obj.valueOf=function(){return 1};
obj.toString=function(){return 0;}
obj == 1; // ?

34. // [Object Object]
alert(new function() {return " "});
// “ ”
alert(new function() {return new String(“
”);});
// Why?
ref: http://www.planabc.net/2008/02/20/javascript_new_function/

35. “new operator”

36. 11.2.2 The new Operator
The production NewExpression : new NewExpression is evaluated as
follows:
1. NewExpression
2. GetValue(Result(1))
3. Type(Result(2)) Object, TypeError
4. Result(2) [[Construct]], TypeError
5. Result(2) [[Construct]]
6. Result(5)

37. 13.2.2 [[Construct]]
When the [[Construct]] property for a Function object F is called,
the following steps are taken:
1.
2. Result(1) [[Class]] "Object"
3. F prototype
4. Result(3) object , Result(1) [[Prototype]]
Result(3)
5. Result(3) object , Result(1) [[Prototype]]
Object prototype ( 15.2.3.1)
6. F [[Call]] Result(1) this
[[Construct]]
7. Type(Result(6)) Object Result(6)
8. Result(1)

38. • History
• Type
• Type Convention
• Examples

39. QA