The example of this article tells the match,charat,charcodeat,map,search usage of JS common difficult point analysis. Share to everyone for your reference, specific as follows:
JavaScript Match () method
Definitions and usage
The match () method retrieves the specified value within a string, or finds a match for one or more regular expressions.
The method is similar to IndexOf () and LastIndexOf (), but it returns the specified value, not the position of the string.
Grammar
Matches a string that returns the specified value
Stringobject.match (Searchvalue) |
Matches regular, returns the specified value
Stringobject.match (RegExp) |
Use Match () to retrieve a string example:
<body> <script type= "Text/javascript" > Varstr= "Hello world!" document.write (Str.match ("World") + "<br/>") document.write (Str.match ("World") + "<br/>") document.write (Str.match ("worlld") + "<br/>") document.write (Str.match ("world!")) </script> </body> |
The result of the final appearance is, world,null,null,world!
Use Match () to retrieve a matching example of a regular expression:
<body> <script type= "Text/javascript" > Varstr= "1 plus 2 equal 3"; The regular expression here must be coupled with G, a global match, or it will match a value that returns document.write (Str.match (/\d+/g)) </script> </body> |
In general, we use match on the top of the more, you can use it to proxy indexof and LastIndexOf to determine whether there is a value in the string.
JavaScript Search () method
Definitions and usage
The search () method retrieves the substring specified in the string, retrieves the substring that matches the regular expression, retrieves the starting position of the returned matching substring, cannot retrieve the value, and returns-1.
Grammar
Stringobject.search (RegExp) |
This parameter can be a substring that needs to be retrieved in Stringobject, or it can be a RegExp object that needs to be retrieved.
To perform a retrieval that ignores case, append the flag I.
Search () Example:
<script type= "Text/javascript" > Varstr= "Visit w3school!" document.write (Str.search (/w3school/)) </script> |
Returns the index value of 6,search is usually used in conjunction with the regular, you can achieve the effect of indexof.
JavaScript charAt () method
Definitions and usage
The CharAt () method returns the character at the specified position.
Note that JavaScript does not have a character data type that is different from a string type, so the character returned is a string of length 1.
Grammar
Returns the string at the specified position
Stringobject.charat (Index) |
Chartat instance:
<script type= "Text/javascript" > Varstr= "Hello world!" document.write (Str.charat (1)) </script> |
The final return result is: E, usually we can get a specific character from a string by Chartat.
JavaScript charCodeAt () method
Definitions and usage
The charCodeAt () method returns the Unicode encoding of the character at the specified position. This return value is an integer between 0-65535.
The method charCodeAt () is similar to the operation performed by the CharAt () method, except that the former returns the encoding of the character at the specified position, and the latter returns a string of characters subcode.
Grammar
Stringobject.charcodeat (Index) |
charCodeAt () instance
Note: The subscript for the first character in the string is 0. If index is a negative number, or is greater than or equal to the length of the string, charCodeAt () returns NaN.
<script type= "Text/javascript" > Varstr= "Hello world!" document.write (Str.charcodeat (1)) Returns the Unicode encoding of H 101 </script> |
Array.prototype.map () method in JS
Definitions and usage
The map () method returns a new array of return values that are composed of each element in the original array calling a specified method.
Grammar
Array.map (callback[, Thisarg]) |
Callback the elements in the original array after the method returns a new element.
The first parameter of the Currentvalue,callback, the element currently being passed in the array.
The second parameter of the Index,callback, the index of the element currently being passed in the array.
The third parameter of the Array,callback, which invokes an array of the map methods.
Thisarg the object that this point is when the callback function is executed.
The map method invokes the callback function in order for each element in the original array. Callback the return value after each execution is grouped together to form a new array. The callback function is invoked only on a valued index, which has never been assigned a value or used
The index deleted by delete is not invoked. The callback function is automatically passed in three parameters: an array element, an element index, and the original array itself.
First example of using map ():
The following code converts all the words in an array to the corresponding plural form.
Functionfuzzyplural (single) { Varresult = Single.replace (/o/g, ' e '); if (single = = ' Kangaroo ') { result = = ' SE '; } Returnresult; } Varwords = ["Foot", "Goose", "Moose", "kangaroo"]; Console.log (Words.map (fuzzyplural)); |
Final results:
["Feet", "geese", "Meese", "Kangareese"] |
To find the square root example of each element in an array
Varnumbers = [1, 4, 9]; Varroots = Numbers.map (MATH.SQRT); /* Roots value is [1, 2, 3], the value of numbers is still [1, 4, 9] * * |
Using the Map method on a string
Varmap = Array.prototype.map Vara = Map.call ("Hello World", function (x) {returnx.charcodeat (0);}) The values for a are [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100] |
<! DOCTYPE html> <meta charset= "UTF-8" > <title></title> <body> <script type= "Text/javascript" > var map = Array.prototype.map Vara = Array.prototype.map.call ("Hello World", function (x) {returnx.charcodeat (0);}) The values for a are [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100] alert (a); </script> </body> |
Map compatible with old environment
A map is a newly added method in the most recent ECMA-262 standard, so some older browsers might not implement the method. In browsers that do not natively support the map method, you can use the following Javascript code to implement it. The algorithm used is ECMA-262, 5th edition. Suppose object, TypeError, and Array have their original values. And the original value of Callback.call is also Function.prototype.call.
| Realize ECMA-262, Edition 5, 15.4.4.19 Reference: http://es5.github.com/#x15.4.4.19 if (! Array.prototype.map) { Array.prototype.map =function (callback, Thisarg) { Vart, A, K; if (this==null) { Thrownewtypeerror ("This is null or not defined"); } 1. Assign o to an array that calls the map method. Varo = Object (this); 2. Assign Len to the length of the array O. Varlen = o.length >>> 0; 4. If callback is not a function, throw the TypeError exception. if ({}.tostring.call (callback)!= "[Object Function]") { Thrownewtypeerror (callback + "is not a function"); } 5. If the parameter thisarg has a value, the T is assigned to THISARG, otherwise t is undefined. if (Thisarg) { T = Thisarg; } 6. Create new array A, length is original array o length len A =newarray (len); 7. Assign K to 0 k = 0; 8. Executes loops when K < Len. while (K < Len) { Varkvalue, Mappedvalue; Traversal O,k is the original array index if (KinO) { Kvalue is the value corresponding to the index K. Kvalue = o[K]; The execution callback,this points to T with three arguments. Kvalue: value, K: Index, O: original array. Mappedvalue = Callback.call (T, Kvalue, K, O); The return value is added to the new book Group A. a[K] = Mappedvalue; } K Self-Increase 1 k++; } 9. Returns the new array a Returna; }; } |
a clever way to generate time stamps usually
The first way
Functiongettimestamp () { Vartimestamp=newdate (). GetTime (); vartimestampstring = timestamp.tostring ()//must convert string Oldtimestamp = timestampstring; returntimestampstring; } |
The second way
Newdate (). toString ()//can achieve the same effect, more concise |
How to use the MD5 encryption method:
Reference GOOGLE,MD5 Encrypted library file: Http://crypto-js.googlecode.com/svn/tags/3.1.2/build/rollups/md5.js
Actually quite simple, inside CRYPTOJS.SHA1 (), direct reference encryption can, give a chestnut:
Just call straight on.
varkeyvaluestring = "DDDDD"; Sign = CRYPTOJS.SHA1 (keyvaluestring). toString (); |
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