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JavaScript Programmer’s Reference Name: null The null value is sometimes used in place of other values. For example, in some browser-based interpreters, there is no specific value for the undefined condition. However, you can work around this by testing for null. Strictly speaking they are distinctly different values with different semantic meanings. Even so, the trick works well enough for most practical purposes. Use nullin place of undefinedwhen testing for the existence of entities. See also: Literal, Range error, Token, undefined Cross-references: ECMA 262 edition 2 section 7.7.1 ECMA 262 edition 3 section 7.8.1 Null statement (Definition) An empty statement consisting of a semicolon on its own. See also: Empty statement (;), Semicolon (;) Number (Primitive value) A built-in primitive value. Availability: Property/method value type: ECMAScript edition 2 Number primitive A number value is a member of the type Number and is a direct representation of a number. It is basically a floating-point number and there is no special integer number class. Integers are simply floating-point values with a zero fractional part. Numbers can be expressed as integers or floating-point values. They can be expressed in decimal, octal, or hexadecimal notation. They can also be expressed in exponential form. Typical limits for the number type allow for very large number values. You can find out what the maximum value is by requesting the MAX_VALUE property from the built-in Number object. It will probably give you a value in the region of 1 followed by some 300 or more zeros. The smallest value is some 300 decimal places past the decimal point. Actually the limits are 1.79e308 down to 5e-324 and both can be positive or negative. 1548

N null (Type) Cross-references: ECMA 262 edition 2 section 4.3.11 ECMA 262 edition 3 section 4.3.11 O’Reilly JavaScript Definitive Guide page 47 null (Type) A native built-in type. Availability: ECMAScript edition 2 Property/method value type: Null primitive The type null has exactly one value, called null. You can use this value when testing for the undefined state of variables and objects in browsers that do not support an explicit undefined value, to test for in logical expressions. See also: Cast operator, Special type, Type Cross-references: ECMA 262 edition 2 section 4.3.12 ECMA 262 edition 2 section 8.2 ECMA 262 edition 3 section 4.3.12 ECMA 262 edition 3 section 8.2 Wrox Instant JavaScript page 14 Null literal (Primitive value) A literal constant whose type is a built-in primitive value. Availability: ECMAScript edition 2 JavaScript 1.5 JScript 5.0 Internet Explorer 5.0 Netscape 6.0 Property/method value type: Null primitive JavaScript syntax: -null The null literal is a value that represents the null or undefined state. It only has one value. 1547

JavaScript Programmer’s Reference Notation.systemId (Property) The system identifier (if one was defined) for this notation. The value may be null if no identifier was defined. Availability: DOM level 1 JavaScript 1.5 JScript 5.0 Internet Explorer 5.0 Netscape 6.0 Property/method value type: String primitive JavaScript syntax: -myNotation.systemId Property attributes: ReadOnly. null (Primitive value) A built-in primitive value. Availability: ECMAScript edition 2 JScript 5.0 Internet Explorer 5.0 Property/method value type: Null primitive JavaScript syntax: IE null The nullvalue is a primitive value that represents the null, empty, or non-existent reference. This is equivalent to the Java nulldata type when passing values back and forth between JavaScript and Java. If you don’t have a null keyword, you may be able to simulate a null value like this: var null = (void 0); The null and undefined values are subtly different. An empty thing is not the same as a nonexistent thing. However in a browser it is difficult to distinguish between them. The nullvalue is now provided in some browsers as a built-in keyword, but the undefined value is not. See also: Cast operator, JavaScript to Java values, LiveConnect, NaN, undefined 1546

N Notation object (Object/DOM) Notation object (Object/DOM) Notations are decalred in the DTD and are encapsulated in these Notation objects. Availability: DOM level 1 JavaScript 1.5 JScript 5.0 Internet Explorer 5.0 Netscape 6.0 Inherits from: Node object JavaScript syntax: -myNotation = new Notation() Object properties: publicId, systemId See also: Doctype object, Doctype.notations[] Property JavaScript JScript N IE Opera DOM Notes publicId 1.5 + 5.0 + 6.0 + 5.0 + 1 + ReadOnly systemId 1.5 + 5.0 + 6.0 + 5.0 + 1 + ReadOnly Inheritance chain: Node object Notation.publicId (Property) The public identifier (if one was defined) for this notation. The value may be null if no identifier was defined. Availability: DOM level 1 JavaScript 1.5 JScript 5.0 Internet Explorer 5.0 Netscape 6.0 Property/method value type: String primitive JavaScript syntax: -myNotation.publicId Property attributes: ReadOnly. 1545

JavaScript Programmer’s Reference Example code: See also: ASCII, Associativity, Equal to (==), Equality expression, Equality operator, Greater than (>), Greater than or equal to (>=), Identically equal to (===), Identity operator, JellyScript, Less than (<), Less than or equal to (<=), Logical expression, Logical operator, NOT Equal to (!=), Operator Precedence, Relational expression, Relational operator, typeof, Unicode Cross-references: ECMA 262 edition 3 section 11.9.5 Wrox Instant JavaScript page 39 1544

N NOT Identically equal to (!==) (Operator/identity) ASCII, Associativity, Equal to (==), Equality expression, Equality operator, Greater than (>), Greater than or equal to (>=), Identically equal to (===), Less than (<), Less than or equal to (<=), Logical expression, Logical NOT complement ( !), Logical operator, NOT Identically equal to (!==), Operator Precedence, Relational expression, Relational operator, typeof, Unicode See also: Cross-references: ECMA 262 edition 2 section 11.9.2 ECMA 262 edition 2 section 11.9.3 ECMA 262 edition 3 section 11.9.2 ECMA 262 edition 3 section 11.9.3 NOT Identically equal to (!==) (Operator/identity) Compare two values for non-equality and identical type. ECMAScript edition 3 JavaScript 1.3 JScript 1.0 Internet Explorer 3.02 Netscape 4.06 anOperand1 A value to be compared anOperand2 Another value of the same type to be compared The two operands are compared and Boolean falseis returned if both values are equal, and of the same type, otherwise Boolean true is returned. The associativity is from left to right. Refer to the Operator Precedence topic for details of execution order. Warnings: .This is not available for use server-side with Netscape Enterprise Server 3. Availability: Property/method value type: JavaScript syntax: - Argument list: Boolean primitive anOperand1 !== anOperand2 1543

JavaScript Programmer’s Reference NOT Equal to (!=) (Operator/equality) Compare two operands for inequality. The two operands are compared, and the Boolean true value is returned if they are not equal, otherwise false if they are equal. Note that JavaScript will attempt to convert both operands to the same type for comparison. When testing for inequality, the following rule is invariant: A != B is equivalent to: !(A == B) Also, the rule of positioning allows that: A == B is identical to: B == A (Apart from the fact that exchanging the operands in this way alters the order in which they are evaluated.) Exchanging the operands may have undesirable side effects if they are expressions. For example, they may call functions and test the results. If the functions are not totally independent of one another, you may get unexpected results. The associativity is from left to right. Refer to the Operator Precedence topic for details of execution order. Refer to the Equality expression topic for a discussion on the ECMA standard definition of the equality testing rules. Availability: ECMAScript edition 2 JavaScript 1.0 JScript 1.0 Internet Explorer 3.02 Netscape 2.0 Netscape Enterprise Server version 2.0 Opera 3.0 Property/method value type: Boolean primitive JavaScript syntax: -anOperand1 != anOperand2 anOperand1 A value to be compared Argument list: anOperand2 Another value to be compared 1542

N NOSCRIPT.dir (Property) Inheritance chain: Element object, Node object NOSCRIPT.dir (Property) The direction of rendering of text contained within the block owned by the

JavaScript Programmer’s Reference IE myNOSCRIPT = myDocument.all.anElementID IE myNOSCRIPT = myDocument.all.tags(”NOSCRIPT”)[anIndex] IE myNOSCRIPT = myDocument.all[aName] -myNOSCRIPT = myDocument.getElementById(anElementID) -myNOSCRIPT = myDocument.getElementsByName(aName)[anIndex] JavaScript syntax: -myNOSCRIPT = myDocument.getElementsByTagName (”NOSCRIPT”)[anIndex] HTML syntax: anIndex A reference to an element in a collection aName An associative array reference Argument list: anElementID The ID value of an Element object Object properties: accessKey, tabIndex, dir Event handlers: onClick, onDblClick, onHelp, onKeyDown, onKeyPress, onKeyUp, onMouseDown, onMouseMove, onMouseOut, onMouseOver, onMouseUp This was added to the MSIE browser at revision 4. It is a sub-class of the basic Element object and therefore shares many properties with other objects in the MSIE browser. Although it is implemented as an Element, it is not a DOM-specified item. See also: Element object, NOFRAMES object Property JavaScript JScript N IE Opera DOM HTML Notes accessKey 3.0 + 4.0 + - tabIndex 3.0 + 4.0 + - dir 5.0 + 5.0 + - Event name JavaScript JScript N IE Opera DOM HTML Notes onClick 3.0 + 4.0 + 4.0 + Warning onDblClick 3.0 + 4.0 + 4.0 + Warning onHelp 3.0 + 4.0 + Warning onKeyDown 3.0 + 4.0 + 4.0 + Warning onKeyPress 3.0 + 4.0 + 4.0 + Warning onKeyUp 3.0 + 4.0 + 4.0 + Warning onMouseDown 3.0 + 4.0 + 4.0 + Warning onMouseMove 3.0 + 4.0 + 4.0 + Warning onMouseOut 3.0 + 4.0 + 4.0 + Warning onMouseOver 3.0 + 4.0 + 4.0 + Warning onMouseUp 3.0 + 4.0 + 4.0 + Warning 1540

N Nondigit (Definition) Nondigit (Definition) A non-digit letter that can be used in an identifier. In the context of creating identifier names, a non-digit character is a member of the following set: a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z _ (Underscore) See also: Digit, Identifier