JavaScript Global method

1. encodeURI (URI)

A, the role: is the Uniform Resource Identifier (URI) encoding method;

B, Parameter: is a complete URI;

C. Features: No need to encode reserved words and characters that have special meaning in the URI.

(1), reserved characters: ; , / ? : @ & = + $

　　　　(2), non-escape character: alphanumeric - _ . ! ~ * ‘ ( )

(3), Mathematical symbols: #

2, decodeURI (Encodeduri)

A, role: decoding a Uniform Resource Identifier (URI) encoded by encodeURI or a similar method;

B, Parameters: a fully encoded URI;

c. Features: converts all the escaped sequences in the encoded URI to the original characters, but does not decode content that is not encoded by encodeURI (for example, "#").

3, encodeURIComponent (str)

A, the role: is the Uniform Resource Identifier (URI) component encoding method;

B, Parameters: String.uri components;

C, feature: Escape all characters except letters, numbers, (,) 、.、!、 ~, *, ',-and _.

4, decodeURIComponent (Encodeduri)

A, role: decoding a Uniform Resource Identifier (URI) encoded by encodeuricomponent or a similar method;

B, Parameters: Part of the URI after encoding;

C. Feature: Converts all the escaped sequences in the encoded URI to the original characters.

5. Eval (str)

A, the role: the incoming string as JavaScript execution;

B, Parameters: strings, expressions that need to be evaluated, or statements executed;

C, return value: Code after the execution of the return value, otherwise undefined;

D, Features: (1), if the parameter is not a string, returned unchanged, (2), direct invocation, using the current scope, indirect invocation, using the global scope.

Eval (new//  Returns a String object containing "2 + 2" //  returns 4function  test () {     var x = 2, y = 4;    Console.log (eval ("x + y"));  // called directly, using the local scope, the result is 6    var geval = eval;    Console.log (Geval (//  Indirect call, using global scope, throws Referenceerror because ' x ' is undefined}

6, Isfinite (testval): Similar to Number.isfinite (TestVal)

A, function: Judge whether the TestVal is a finite value;

B, Parameter: Incoming string, will be converted into a number to judge. Note: number.isfinite (testval) does not convert the type.

C, return value: True/false;

Isfinite (Infinity);//falseIsfinite (-infinity);//falseIsfinite (0);//trueIsfinite (2E64);//trueIsfinite ("0");//trueIsfinite (NaN);//falseIsfinite (NULL);//trueIsfinite (undefined);//falseIsfinite (true);//trueIsfinite (false);//trueNumber.isfinite (Infinity); //falseNumber.isfinite (-infinity);//falseNumber.isfinite (0);//trueNumber.isfinite (2E64);//trueNumber.isfinite ("0");//falseNumber.isfinite (NaN);//falseNumber.isfinite (NULL);//falseNumber.isfinite (undefined);//falseNumber.isfinite (true);//falseNumber.isfinite (false);//false

7, IsNaN (TestVal)

A, the role: Determine whether a value is Nan, the argument is cast to a number and then judged.

B, return value: True/false

C, Characteristics: (1), Nan can not be determined by = = and = = =, Nan = = nan and Nan = = = Nan all return False, (2), arithmetic operations get a value that cannot be represented or undefined, is Nan, (3), cannot force a newline into a number, is Nan; (4), 0 divided by 0 will return nan--but the other number divided by 0 will not return Nan.

Escape (), unescape (): Abandoned.

D, Note: It is a reliable practice to detect whether a variable x is a non-numeric value by Number.isnan (x). However, in the absence of the Number.isnan function, it is more reliable to detect if the variable x is Nan by means of an expression (x! = x).

IsNaN =function(value) {Number.isnan (number);}       IsNaN (NaN); //trueIsNaN (undefined);//trueIsNaN ({});//trueIsNaN (0/0);//trueIsNaN (5/0);//falseIsNaN (true);//falseIsNaN (NULL);//falseIsNaN (37);//falseIsNaN ("37");//false: Can be converted to a number of PNSIsNaN ("37.37");//false: Can be converted to numeric 37.37IsNaN ("");//false: An empty string is converted to 0IsNaN ("");//false: A string containing spaces is converted to 0IsNaN (NewDate ());//falseIsNaN (NewDate (). toString ());//trueIsNaN ("BlaBla")//true: "BlaBla" cannot be converted to a numeric value//compared to the global function IsNaN (), this method does not force the parameter to be converted to a number, and returns true only if the parameter is a true numeric type and the value is NaN. Number.isnan (NaN);//trueNumber.isnan (undefined);//falseNumber.isnan ({});//falseNumber.isnan (0/0);//trueNumber.isnan (5/0);//falseNumber.isnan (true);//falseNumber.isnan (NULL);//falseNumber.isnan (37);//falseNumber.isnan ("37");//false: cannot be converted to a value of PNsNumber.isnan ("37.37");//false: cannot be converted to numeric 37.37Number.isnan ("");//false: No empty string is converted to 0Number.isnan ("");//false: Strings that do not contain spaces are converted to 0Number.isnan (NewDate ());//falseNumber.isnan (NewDate (). toString ());//falseNumber.isnan ("BlaBla")//false: "BlaBla" cannot be converted to a numeric value

8, null and undefined

A, null:javascript literal, one of the original JavaScript values, representing the null value, not the property of the global object

B, Undefined:javascript one of the original values, is the raw data type of JavaScript, is the property of the global object

typeof NULL        //object (because of some previous reason rather than ' null ')typeofUndefined//undefinedNULL= = = undefined//falseNULL= = undefined//trueNULL===NULL //trueNULL==NULL //true!NULL //trueIsNaN (1 +NULL)//falseIsNaN (1 + undefined)//true

9, parseint and parsefloat

A, parseint: Returns an integer

B, parsefloat: Returns a floating-point number

JavaScript Global method