The fun of JavaScript--0220

1, for the generator function, is not very understanding, and then continued

2. JavaScript Fun _ Don't ask why

• Do not use new number () , new Boolean () , new String () to create the wrapper object;

• Use parseint () or parsefloat () to convert any type to number ;

• To use string () to convert any type to string , or to invoke the toString () method of an object directly;

• Usually does not have to convert any type to Boolean , because you can directly write if (MyVar) {...}

• typeof operator to determine the number , boolean , string , function and undefined ;

• Judging Array to use Array.isarray (arr) ;

• Judge null use MyVar = = = null ;

• Determine if a global variable exists typeof Window.myvar = = = ' undefined ' ;

• Function internally to determine whether a variable exists with typeof MyVar = = ' undefined ' .

1 // SyntaxError

// ' 123 ', attention is two points!  //  ' 123 '

2, for the Date object, a place where the father of the hole is the JavaScript month range is represented by an integer 0~11, which represents 0 January, 1 February ..., so to say June, we passed in 5 !

1 var New Date (); 2 if (Today.getmonth () = = = 2 && today.getdate ()= = =3     alert (' Dear, I've booked dinner, I'll meet you at the restaurant 6 o'clock in the evening! '); 4 }

The above code, really is the rhythm of solitary born ah ... Because it matches the March 14 (the pit is everywhere).

3, REGEXP (regular expression)

• ‘00\d‘Can match ‘007‘ , but cannot match ‘00A‘ ;

• ‘\d\d\d‘can match ‘010‘ ;

• ‘\w\w‘can match ‘js‘ ;

.Can match any character, so:

• ‘js.‘Can match ‘jsp‘ , ‘jss‘ ,‘js!‘

To match a variable-length character, in a regular expression, with a representation of * any character (including 0), with a representation of + at least one character, representing ? 0 or 1 characters, with a representation of {n} n characters, represented by {n,m} n-m characters:

Advanced:

• [0-9a-zA-Z\_]Can match a number, letter, or underscore;

• [0-9a-zA-Z\_]+Can match a string of at least one number, letter, or underscore, for example, and ‘a100‘ ‘0_Z‘ ‘js2015‘ so on;

• [a-zA-Z\_\$][0-9a-zA-Z\_\$]*You can match a string consisting of a number, letter, or underscore, or $, which is the name of the variable allowed by JavaScript, by a letter or underscore, or $.

• [a-zA-Z\_\$][0-9a-zA-Z\_\$]{0, 19}More precisely limit the length of a variable to 1-20 characters (1 characters before + 19 characters later).

A|BCan match A or B, so (J|j)ava(S|s)cript you can match ‘JavaScript‘ , ‘Javascript‘ , ‘javaScript‘ or ‘javascript‘ .

^Represents the beginning of a row, ^\d indicating that a number must begin.

$Represents the end of a line, indicating that it \d$ must end with a number.

You may have noticed it, but you can match it, js ‘jsp‘ but plus ^js$ it turns into an entire line match, it only matches ‘js‘ .

1 var re1 =/abc\-001/; 2 var New REGEXP (' abc\\-001 '); 3 4 // /abc\-001/ 5 // /abc\-001/

The method of the RegExp object test() is used to test whether a given string meets the criteria

1 var re =/^\d{3}\-\d{3,8}$/; 2 // true 3 // false 4 // false

To slice a string:

1 ' A, b;; C  //  [' A ', ' B ', ' C ', ' d ']

grouping, greedy matching, global matching and searching

A. ^(\d{3})-(\d{3,8})$ Two groups are defined, and the area code and local numbers can be extracted directly from the matching string

  exec()After the match succeeds, the method returns one Array , the first element is the entire string to which the regular expression matches, and the subsequent string represents the successful substring.

  exec()Method is returned when a match fails null .

1 var re =/^ (\d{3})-(\d{3,8}) $/; 2 // [' 010-12345 ', ' 010 ', ' 12345 '] 3 // NULL

B. Regular matching is a greedy match by default, which is to match as many characters as possible

1 var re =/^ (\d+) (0*) $/; 2 // [' 102300 ', ' 102300 ', ']

Let \d+ a non-greedy match (that is, as few matches as possible) to the back of the 0 match out, add a ? can let \d+ the use of non-greedy matching

1 var re =/^ (\d+?) (0*) $/; 2 // [' 102300 ', ' 1023 ', ' xx ']

C.javascript Regular expressions also have several special flags, most commonly g , representing global matches, and global matching can execute methods multiple times exec() to search for a matching string. When we specify a g flag, each time it is run exec() , the regular expression itself updates the lastIndex property to indicate the last index to which it was last matched

1 vars = ' JavaScript, VBScript, JScript and ECMAScript ';2 varre=/[a-za-z]+script/G;3 4 //use global match:5Re.exec (s);//[' JavaScript ']6Re.lastindex;//Ten7 8Re.exec (s);//[' VBScript ']9Re.lastindex;// -Ten  OneRe.exec (s);//[' JScript '] ARe.lastindex;// in -  -Re.exec (s);//[' ECMAScript '] theRe.lastindex;// - -  -Re.exec (s);//NULL until the end is still not matched to

The regular expression can also specify i flags, which indicate that the case is ignored, the m flag, indicating that a multiline match is performed

Example: matching email address:

1 varRe =/^[\da-za-z]+ ([. _-]\w+) *@ ([\da-za-z]+\.) +[a-za-z]{2,6}$/;2 3 varRe =/^< (. +?) >\s* ([\da-za-z]+[._-]?\[email protected][\da-za-z]+\.[ a-za-z]{2,6}) $/;//Group to get an email address part of the content4 5 //Test section:6 //Test:7 varr = re.exec (' <tom paris> [email protected] ');8 if(r = =NULL|| R.tostring ()!== [' <tom paris> [email protected] ', ' Tom Paris ', ' [email protected] '].tostring ()) {9Alert (' Test failed! '));Ten } One Else { AAlert (' Test succeeded! ')); -}

The fun of JavaScript--0220