JavaScript advanced programming book note 11 built-in object Global

Built-in object
Definition: all objects provided by ECMAScript and independent from the host environment are displayed when the ECMAScript program starts to run.

It can be seen from the definition that the developer does not need to explicitly instantiate the built-in object, and it has been instantiated. Only two built-in objects, Global and Math, are defined in the ECMAScript-262

Global
Global objects are the most special objects in ECMAScript, because they do not exist at all.

Because no independent object exists in ECMAScript, all functions must be methods of an object, such as isNaN (), isFinite (), parseInt (), and parseFloat, all are Global object methods.

Escape (), encodeURI (), encodeURIComponent (), unescape (), decodeURI (), decodeURIComponent (), and eval () are all Global methods.

Escape () & encodeURI () & encodeURIComponent ()
These methods are used to encode strings.

Escape unencoded characters are 69: *, +,-,.,/, @, _, 0-9, a-z, A-Z

EncodeURI is not encoded with 82 characters :!, #, $, &, ', (,), *, +,-,.,/,:,;, = ,?, @,_,~, 0-9, a-z, A-Z

EncodeURIComponent has 71 unencoded characters :!, ',(,),*,-,.,_,~, 0-9, a-z, A-Z

　　Escape (): not recommended, eliminated

EncodeURI (): encode the URL, for example:
Copy codeThe Code is as follows:
EncodeURI ("http://www.jb51.net/a file with spaces.html ")
// Outputs http://www.jb51.net/a%20file%20with%20spaces.html

EncodeURIComponent (): encode the parameter, for example:
Copy codeThe Code is as follows:
Param1 = encodeURIComponent ("http://xyz.com /? A = 12 & B = 55 ")
Url = "http://domain.com /? Param1 = "+ param1 +" & param2 = 99 ";
// Outputs http://www.domain.com /? Param1 = http % 3A % 2F % 2Fxyz.com % 2F % Ffa % 3D12% 26b % 3D55 & param2 = 99

Unescape () & decodeURI () & decodeURIComponent ()
These methods are used to decode strings.

Eval ()
Eval () may be the most powerful method in the ECMAScript language. This method is like an entire JavaScript interpreter that accepts a parameter, that is, the ECMAScript (or JavaScript) string to be executed.

Example:

Copy codeThe Code is as follows:
Var msg = "Hello world ";
Eval ("alert (msg)"); // alert "Hello world"

Note that eval () is powerful but dangerous, especially when using eval to execute user input content, it may be injected by code.

All attributes of the Global Object
Global does not only have methods, but also has all attributes of the Global object:

Attribute	Description
Undefined	UndifinedType literal
NaN	Non-numeric value
Infinity	Special Value of an infinite value
Object	ObjectConstructor
Array	ArrayConstructor
Function	FunctionConstructor
Boolean	BooleanConstructor
String	StringConstructor
Number	NumberConstructor
Date	DateConstructor
RegExp	RegExpConstructor
Error	ErrorConstructor
EvalError	EvalErrorConstructor
RangeError	RangeErrorConstructor
ReferenceError	ReferenceErrorConstructor
SyntaxError	SyntaxErrorConstructor
TypeError	TypeErrorConstructor
URIError	URIErrorConstructor

Author: tianxingjian, self-improvement

Source: http://artwl.cnblogs.com