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Global

The Global object is the parent of all globally avaliable properties and methods.

Platform Support

IE Mozilla Netscape Opera Safari
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Constructors

Constructor Action IE Mozilla Netscape Opera Safari
Global Constructor() : Object
The Global object does not have a constructor.
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Global() : Object

The Global object does not have a constructor.

Returns

Object

Properties

Property Action IE Mozilla Netscape Opera Safari
static Infinity : Infinity
A numeric value representing infinity.
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Remarks

Infinity is a property of the global object, i.e. it is a variable in global scope.

The initial value of Infinity is Number.POSITIVE_INFINITY. The value Infinity (positive infinity) is greater than any other number including itself. This value behaves mathematically like infinity; for example, anything multiplied by Infinity is Infinity, and anything divided by Infinity is 0.

See Also

Number.NEGATIVE_INFINITY|Number.POSITIVE_INFINITY

Availability

JavaScript 1.3|JScript 3.0|ECMAScript v1

NaN : NaN
A value representing Not-a-Number.
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Remarks

NaN is a property of the global object, i.e. it is a variable in global scope.

The initial value of NaN is Not-A-Number - the same as the value of Number.NaN.

NaN is always unequal to any other number, including NaN itself; you cannot check for the not-a-number value by comparing to Number.NaN. Use the isNaN function instead.

Several JavaScript methods (such as the Number constructor, parseFloat, and parseInt) return NaN if the value specified in the parameter can not be parsed as a number.

You might use the NaN property to indicate an error condition for your function that returns a number in case of success.

JavaScript prints the value Number.NaN as NaN.

See Also

isNaN|Number.NaN

Availability

JavaScript 1.3|JScript 3.0|ECMAScript v1

undefined : undefined
The value undefined.
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Remarks

undefined is a property of the global object, i.e. it is a variable in global scope.

The initial value of undefined is the primitive value undefined.

A variable that has not been assigned a value is of type undefined. A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not returned.

You can use undefined and the strict equality operator to determine whether a variable has a value. In the following code, the variable x is not defined, and the if statement evaluates to true.

var x;
                        if (x === undefined) {
                        // these statements execute
                        }
                        

Note: The strict equality operator rather than the standard equality operator must be used here, because x == undefined also checks whether x is null, while strict equality doesn't. null is not equivalent to undefined. See comparison operators for details.

Alternatively, typeof can be used:

var x;
                        if (typeof x == 'undefined') {
                        // these statements execute
                        }
                        
Availability

JavaScript 1.3|JScript 5.5|ECMAScript v1

Functions

Method Action IE Mozilla Netscape Opera Safari
decodeURI(String encodedURI) : String
Decodes a Uniform Resource Identifier (URI) previously created by encodeURI or by a similar routine.
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Parameters

String encodedURI A complete, encoded Uniform Resource Identifier.

Returns

String
Remarks

Replaces each escape sequence in the encoded URI with the character that it represents.

Does not decode escape sequences that could not have been introduced by encodeURI.

See Also

decodeURIComponent|encodeURI|encodeURIComponent

Availability

JavaScript 1.5|JScript 5.5|ECMAScript v3

decodeURIComponent(String encodedURI) : String
Decodes a Uniform Resource Identifier (URI) component previously created by encodeURIComponent or by a similar routine.
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Parameters

String encodedURI An encoded component of a URI.

Returns

String
Remarks
Replaces each escape sequence in the encoded URI component with the character that it represents.
See Also

decodeURI|encodeURI|encodeURIComponent

Availability

JavaScript 1.5|JScript 5.5|ECMAScript v3

encodeURI(String URI) : String
Encodes a Uniform Resource Identifier (URI) by replacing each instance of certain characters by one, two, or three escape sequences representing the UTF-8 encoding of the character.
Show Details 5.5+ 1.0+ 6.0+ 7.0+ no

Parameters

String URI A complete Uniform Resource Identifier.

Returns

String
Remarks

Assumes that the URI is a complete URI, so does not encode reserved characters that have special meaning in the URI.

encodeURI replaces all characters except the following with the appropriate UTF-8 escape sequences:

Type Includes
Reserved characters ; , / : @ & = + $
Unescaped characters alphabetic, decimal digits, - _ . ! ~ * ' ( )
Score #

Note that encodeURI by itself cannot form proper HTTP GET and POST requests, such as for XMLHTTPRequests, because "&", "+", and "=" are not encoded, which are treated as special characters in GET and POST requests. encodeURIComponent, however, does encode these characters. These behaviors are most likely not consistent across browsers.

See Also

decodeURI|decodeURIComponent|encodeURIComponent

Availability

JavaScript 1.5|JScript 5.5|ECMAScript v3

encodeURIComponent(String String) : String
Encodes a Uniform Resource Identifier (URI) component by replacing each instance of certain characters by one, two, or three escape sequences representing the UTF-8 encoding of the character.
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Parameters

String String A component of a Uniform Resource Identifier.

Returns

String
Remarks

encodeURIComponent escapes all characters except the following: alphabetic, decimal digits, - _ . ! ~ * ' ( )

For security reasons, you should call encodeURIComponent on any user-entered parameters that will be passed as part of a URI. For example, a user could type "Thyme &time=again" for a variable comment. Not using encodeURIComponent on this variable will give comment=Thyme%20&time=again. Note that the ampersand and the equal sign mark a new key and value pair. So instead of having a POST comment key equal to "Thyme &time=again", you have two POST keys, one equal to "Thyme " and another (time) equal to again. This is super, super, super dangerous if you are using PHP with register_globals turned on.

See Also

decodeURI|decodeURIComponent|encodeURI

Availability

JavaScript 1.5|JScript 5.5|ECMAScript v3

escape(string string) : String
Returns a URI-encoded version of a string.
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Parameters

string string String to be URI-encoded.

Returns

String
Remarks
escape has been phased out in favor of encodeURIComponent.
See Also

unescape|encodeURIComponent

Availability

JavaScript 1.0|JScript 1.0

eval(String string) : Boolean|Number|Object|String
Evaluates a string of JavaScript code without reference to a particular object.
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Parameters

String string A string representing a JavaScript expression, statement, or sequence of statements. string can include variables and properties of existing objects.

Returns

Boolean
Number
Object
String

The following examples display output using document.write. In server-side JavaScript, you can display the same output by calling the write function instead of using document.write.

Example: Using eval

In the following code, both of the statements containing eval return 42. The first evaluates the string "x + y + 1"; the second evaluates the string "42".

var x = 2;
                        var y = 39;
                        var z = "42";
                        eval("x + y + 1"); // returns 42
                        eval(z);           // returns 42 
                        

Example: Using eval to evaluate a string of JavaScript statements

The following example uses eval to evaluate the string str. This string consists of JavaScript statements that open an Alert dialog box and assign z a value of 42 if x is five, and assigns 0 to z otherwise. When the second statement is executed, eval will cause these statements to be performed, and it will also evaluate the set of statements and return the value that is assigned to z.

var str = "if (x == 5) {alert('z is 42'); z = 42;} else z = 0; ";
                        document.write("

z is ", eval(str));

Remarks

eval is a top-level function and is not associated with any object.

The argument of the eval function is a string. If the string represents an expression, eval evaluates the expression. If the argument represents one or more JavaScript statements, eval performs the statements. Do not call eval to evaluate an arithmetic expression; JavaScript evaluates arithmetic expressions automatically.

If you construct an arithmetic expression as a string, you can use eval to evaluate it at a later time. For example, suppose you have a variable x. You can postpone evaluation of an expression involving x by assigning the string value of the expression, say "3 * x + 2", to a variable, and then calling eval at a later point in your script.

If the argument of eval is not a string, eval returns the argument unchanged. In the following example, the String constructor is specified, and eval returns a String object rather than evaluating the string.

eval(new String("2+2")); // returns a String object containing "2+2"
                        eval("2+2");             // returns 4
                        

You cannot indirectly use the eval function by invoking it via a name other than eval; if you do, a runtime error might occur. For example, you should not use the following code:

var x = 2;
                        var y = 4;
                        var myEval = eval;
                        myEval("x + y");
                        

You should not use eval to convert property names into properties. For example, consider the following example. The getFieldName(n) function returns the name of the specified form element as a string. The first statement assigns the string value of the third form element to the variable field. The second statement uses eval to display the value of the form element.

var field = getFieldName(3);
                        document.write("The field named ", field, " has value of ",
                        eval(field + ".value"));
                        

However eval is not necessary here. In fact, its use here is discouraged. Instead, use the member operators, which are much faster:

var field = getFieldName(3);
                        document.write("The field named ", field, " has value of ",
                        field[value]);
                        

Backward Compatibility

JavaScript 1.3 and earlier

You can use eval indirectly, although it is discouraged.

JavaScript 1.1

eval is also a method of all objects.

Availability

JavaScript 1.0|JScript 1.0|ECMAScript v1

isFinite(Number number) : Boolean
Evaluates whether an argument is a finite number.
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Parameters

Number number Number to be evaluated.

Returns

Boolean

Example: Using isFinite

You can check a client input to determine whether it is a finite number.

if (isFinite(ClientInput)) {
                        /* take specific steps */
                        }
Remarks

isFinite is a top-level function and is not associated with any object.

You can use this method to determine whether a number is a finite number. The isFinite method examines the number in its argument. If the argument is NaN, positive infinity or negative infinity, this method returns false, otherwise it returns true.

See Also

Number.NEGATIVE_INFINITY|Number.POSITIVE_INFINITY

Availability

JavaScript 1.3|JScript 3.0|ECMAScript v1

isNaN(String value) : Boolean
Evaluates whether an argument is NaN.
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Parameters

String value The value you want to evaluate.

Returns

Boolean

Example: Using isNaN

The following example evaluates floatValue to determine if it is a number, and then calls a procedure accordingly:

floatValue = parseFloat(toFloat);
                        
                        if (isNaN(floatValue)) {
                        notFloat();
                        } else {
                        isFloat();
                        }
Remarks

isNaN is a top-level function and is not associated with any object.

The parseFloat and parseInt functions return NaN when they evaluate a value that is not a number. isNaN returns true if passed NaN, and false otherwise.

This function is necessary, because the value NaN cannot be meaningfully tested with the equality operators. x == NaN and x === NaN are always false, regardless of what x is, even if x is NaN. For example, both 1 == NaN and NaN == NaN return false.

See Also

Number.NaN|parseFloat|parseInt

Availability

JavaScript 1.1|JScript 3.0|ECMAScript v1

parseFloat(String string) : Number
Parses a string and returns its value as a number.
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Parameters

String string A string that represents the value you want to parse.

Returns

Number

Example: parseFloat returning a number

The following examples all return 3.14:

  • parseFloat("3.14");
  • parseFloat("314e-2");
  • parseFloat("0.0314E+2");
  • var x = "3.14";
    parseFloat(x);
  • parseFloat("3.14more non-digit characters");

Example: parseFloat returning NaN

The following example returns NaN:

  • parseFloat("FF2");
Remarks

parseFloat is a top-level function and is not associated with any object.

parseFloat parses its argument, a string, and returns a floating point number. If it encounters a character other than a sign (+ or -), numeral (0-9), a decimal point, or an exponent, it returns the value up to that point and ignores that character and all succeeding characters. Leading and trailing spaces are allowed.

If the first character cannot be converted to a number, parseFloat returns NaN.

For arithmetic purposes, the NaN value is not a number in any radix. You can call the isNaN function to determine if the result of parseFloat is NaN. If NaN is passed on to arithmetic operations, the operation results will also be NaN.

See Also

isNaN|parseInt

Availability

JavaScript 1.0|JScript 1.0|ECMAScript v1

parseInt(String string, [Number radix]) : Number
Parses a string argument and returns an integer of the specified radix or base.
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Parameters

String string A string that represents the value you want to parse.
Number radix (optional)An integer that represents the radix of the above mentioned string.

Returns

Number

Example: Using parseInt

The following examples all return 15:

  • parseInt("F", 16);
  • parseInt("17", 8);
  • parseInt("15", 10);
  • parseInt(15.99, 10);
  • parseInt("FXX123", 16);
  • parseInt("1111", 2);
  • parseInt("15*3", 10);
  • parseInt("12", 13);

The following examples all return NaN:

  • parseInt("Hello", 8); // Not a number at all
  • parseInt("0x7", 10); // Not in base 10 format
  • parseInt("546", 2); // Digits are not valid for binary representations

Even though the radix is specified differently, the following examples all return 17 because the input string begins with "0x".

  • parseInt("0x11", 16);
  • parseInt("0x11", 0);
  • parseInt("0x11");
Remarks

parseInt is a top-level function and is not associated with any object.

The parseInt function parses its first argument, a string, and attempts to return an integer of the specified radix (base). For example, a radix of 10 indicates to convert to a decimal number, 8 octal, 16 hexadecimal, and so on. For radixes above 10, the letters of the alphabet indicate numerals greater than 9. For example, for hexadecimal numbers (base 16), A through F are used.

If parseInt encounters a character that is not a numeral in the specified radix, it ignores it and all succeeding characters and returns the integer value parsed up to that point. parseInt truncates numbers to integer values. Leading and trailing spaces are allowed.

If the radix is not specified or is specified as 0, JavaScript assumes the following:

  • If the input string begins with "0x", the radix is 16 (hexadecimal).
  • If the input string begins with "0", the radix is eight (octal). This feature is deprecated.
  • If the input string begins with any other value, the radix is 10 (decimal).

If the first character cannot be converted to a number, parseInt returns NaN.

For arithmetic purposes, the NaN value is not a number in any radix. You can call the isNaN function to determine if the result of parseInt is NaN. If NaN is passed on to arithmetic operations, the operation results will also be NaN.

See Also

isNaN|parseFloat|Object.valueOf

Availability

JavaScript 1.0|JScript 1.0|ECMAScript v1

unescape(String string) : String
Returns a URI-decoded version of a string.
Show Details 3.0+ 1.0+ 2.0+ 7.0+ 1.0+

Parameters

String string URI-encoded string to be decoded.

Returns

String
Remarks
unescape has been phased out in favor of decodeURIComponent.
See Also

escape|decodeURIComponent

Availability

JavaScript 1.0|JScript 1.0

Availability

JavaScript 1.0|JScript 1.0|ECMAScript v1

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