Javascript Programming Tips Summary (part of the content for reference to others)

-use = = = instead of = =

the = = (or! =) operator automatically performs type conversions when needed. the = = = (or!==) operation does not perform any conversions. It compares values and types, and is considered better at speed than = =.

--using closures to implement private variables

function fn1 () {   var pro1= "a";   This.fn2=function () {return pro1;}}

3-Get a random item from the array　

<script>       var items = [548, ' a ', 2, 5478, ' foo ', 8852,, ' Doe ', 2145, 119,11];       var  randomitem = Items[math.floor (Math.random () * items.length)]; </script>

4– get a random number within a specific range

This code snippet is useful when you want to generate test data, such as a random salary value between the minimum and maximum values.

var x = Math.floor (Math.random () * (Max-min + 1)) + min;

5– generates a random numeric alphabetic string

function Generaterandomalphanum (len) {    var rdmstring = "";    for (; rdmstring.length < Len; rdmstring  + = Math.random (). toString (. substr (2));    return  rdmstring.substr (0, Len);}

6 – Scramble a numeric array

var numbers = [5, 458, -215, 228, 122205, -85411];numbers = Numbers.sort (function () {return math.random ()- 0.5});/* The array numbers would be equal for example to [5, 228, -215, 458, 122205, -85411,]  */

Trim function of 7–string

There is a classic trim function in Java, C #, PHP, and many other languages to remove the whitespace from the string, not in JavaScript, so we need to add this function to the string object.

String.prototype.trim = function () {return this.replace (/^\s+|\s+$/g, "");};

8– verify whether the parameter is a number

function Isnumber (n) {    return!isnan (parsefloat (n)) && isfinite (n);}

9– Verify if the parameter is an array

10– gets the maximum or minimum value in a numeric array

var  = [5, 458, -215, 228, Numbers, 122205, -85411];var maxinnumbers = Math.max.apply (Math, numbers); var Mininnumbers = Math.min.apply (Math, numbers); "Note: Here are the techniques for passing parameters using the Function.prototype.apply method"

11– empty An array

12– do not use Delete to delete an item in an array.

Use splice instead of Delete to remove an item from the array. Using delete simply replaces the original item with undefined, not the actual deletion from the array. The Delete method should be used to delete a property of an object.

13– rounding a number, preserving n decimal places

Str.tofixed (2);

14– floating point problem

Why is that? 0.1+0.2 equals 0.30000000000000004. You know, all of the JavaScript numbers are internally floating numbers in 64-bit binary notation, conforming to the IEEE 754 standard. For more information, you can read this blog post. You can use the toFixed () and Toprecision () methods to solve this problem.

15– checking properties when using For-in to traverse an object's internal properties

for (var name in object) {    if (Object.hasownproperty (name)) {        //does something with name    }}

16– comma operator

var a = 0;var B = (a++); Console.log (a);  A'll is equal to 1console.log (b);  B is equal to 99

-JSON-based serialization and deserialization (serialization and deserialization)

var person = {name: ' Saad ', age:26, department: {id:15, Name: "R & R"}};var Stringfromperson = Json.stringify (per son);/* Stringfromperson is equal to ' {' name ': ' Saad ', ' age ': ', ' Department ': {' ID ': ' Name ': ' R '}} '   */var personfromstring = Json.parse (Stringfromperson);/* personfromstring is equal to Person object  */

　　

18– Pass in the function when calling SetTimeout () and setinterval (), not the string.

If you pass the string to SetTimeout () or setinterval (), the string will be parsed as if it were using eval, which is very time consuming.
Do not use:

SetInterval (' dosomethingperiodically () ', +), SetTimeOut (' Dosomethingafterfiveseconds () ', 5000);

And with

SetInterval (dosomethingperiodically), SetTimeOut (Dosomethingafterfiveseconds, 5000);

-Keep in mind that primitive operators are always more efficient than function calls.

Do not var min = Math.min (A, b); A.push (v);//var min = a < b? A b; A[a.length] = v;

　　

Javascript Programming Tips Summary (part of the content for reference to others)