The sixth day of learning JS

some knowledge review and notes learned today

1. Regular Expressions (REGEXP)

1.1 notation

/the contents of the regular expression/

Example:/^\w{6,10}\@[0-9a-z]{1,4}.com$/, this is a regular expression, simple validation of the mailbox format expression.

Let's explain the example below:

(1) ^: The beginning of the regular expression.

(2) $: The end of the regular expression.

(3) \w: Represents numbers, letters, and underscores.

(4) {6,10}: Curly braces represent the number of digits, meaning 6 to 10 bits, which means that the preceding \w is 6 to 10 bits.

(5) \@: The escape character "\" plus a special symbol means matching this character. If they are not special characters in the regular expression (such as "^" and "$", etc.), they can be used without the escape character.

(6) [0-9a-z]: curly braces represent the range, which represents any number from 0 to 9 and any letter from A to Z.

(7) {1,4}: Same as above {6,10}.

There are also some frequently used:

(8) \d: The expression is [0-9].

(9) \s: space

(Ten) \d: matches except for numbers.

\w: In contrast to \w, matches except numbers, letters, and underscores.

\s: In contrast to \s, matches except for spaces.

(13) +: Indicates 1 to more bits, {1,}

(14) *: Indicates 0 or more digits.

(15) ".": Indicates that all of the matches are matched.

1.2 Methods

(1) test (): Tests for matching objects.

An example of a matching month:
var month = "12";
var val =/0[1-9]|1[0-2]/; The month is 1-9 months and 10, 11, December, so there are 0 months or 1 months. "|" Represents or.
var result = val.test (month); Method of the regular expression test, testing the string variable month.
Console.log (result); The console will output true, and if you change month to 13, it will return false.

(2) EXEC (): Matches what shows what, returns an array where the matching results are stored. If no match is found, the return value is null.

var str = "23342addff#"
var reg =/[0-9a-z]\#/
var re = reg.exec (str);
Console.log (re); Display array [F #], connected to match, for example, the first five in the STR variable is a number, followed by five is the letter, the last is # if the reg is stored in the/[0-9]{5}\#/, the console display is null. Because the numbers and # are not directly connected, this will not match.

1.3 Applications

(1) Join (): Concatenate the strings in the array, and you can write the custom connector in parentheses.

var arr = ["Hello", "World", "!"];
var re = Arr.join ("$"); For the array arr is connected with the "$" symbol.
Console.log (re); Shows the hello$world$!.

(2) Split (): Split score Group

var str = "[email protected]";
var val =/[@-]/;
var re = Str.split (val); For string str, retrieves the symbols in the regular expression in the string and separates them in an array form.
Console.log (re); Show array["2015", "12", "20"]

2.toString ()

　　　　The ToString () method converts a logical value to a string and returns the result.

Cases:

var num = 12343;
var str = num.tostring ();
Console.log (str); Showing 12343
Console.log (typeof (str));//Display string

　　3. About closure issues

1. Function assignment has a return value
         var a = function () {   //Assign a function to a, now a is a function.
              return "Hello";   // The return value hello.   If this sentence is commented out, then the value of B below is undefined, because there is no return value, this function will not get any value even if B is executed. The following is written if no return value is in the case.
        }
         A (); //Call function a
         var b = A ();  //define B for the value returned by this function A.
        console.log (b);    //console will display Hello

2. Immediate function has return value
       var a = function () {            //a is assigned the return value of the immediate function, and a is not a function.　　　　
             return "haha"
         } ()
        var b = a;  //So here A is directly equal to B, not a ().
         Console.log (b);   //display haha

3. The non-immediate function does not return a value.
             var a = function () {   //Assign a function to a, Now a is a function.
            }
        a (); //Call function a
         var b = A ();  //define B for the value returned by this function A.
         Console.log (b);  //display undefined because function A does not return a value.

4. Immediate function does not return a value case
var a = function () {//a is assigned to the return value of the immediate function, and a is not a function.
}()
var B = A; So here A is directly equal to B, not a ().
Console.log (b); The undefined is also shown here.

　　　　In summary, if the function does not return a value, whether the function is immediately executed or not immediately execute the function is not a value, only executes the code in the function body, non-immediate functions need to call the function to execute. If a function has a return value, if a non-immediate function is given a variable B, then B equals the return value of the function, and if the function is executed immediately, then B is immediately executing the function's return value.

The sixth day of learning JS