To Compare Float, Double, or Long Data Types

A way to make doubles, floats, or longs ‘equal’.

Float a=1.56148; Float b=1.56139;
  Float threshold = 0.00009 or 0.0001 //difference of Float a and Float b
  if (Math.abs(a-b) <= threshold){//Or < threshold
     //logic here
  }

JSON Serialization: JS Object to JSON Data (Strings)

//Systax: var myJSONText=JSON.stringify(myObject,replacer);
   //claim a JS object
   var jsonObj=[
      name:'aaa',
      age:444,
      lv:22
   },{
      name:'bbb',
      age:255,
      lv:1
   }]
 

JavaScript: AJAX Basic

function ajax(){
   //1.Creat Ajax object
   var myAjax=new XMLHttpRequest()

   //XMLHttpRequest is the core object of Ajax
   //alert(myAjax);//Doesn't support IE6 or older version

   //2.Connect to Server
   //open(function，file path，file transfer)true is to transfer file
    myAjax.open('GET','ReadMe.docx','true');

   //3.send request
    myAjax.send(null);
 

JavaScript: JSON data store

Way to store and read JSON, similar to XML
JSON can be used in almost all programming languages
JSON is easy to understand

//Way to show JavaScript Object
var user={
   name:'KK',
   age:'20'
}
 

JavaScript AJAX: Fetch JSON Data

Include ajax link in script tag, link：https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js

JavaScript code:
   function ajaxJson(){
      //Calling a functin from an existing JS file
      ajaxFn('data.json',function(str){//Valid JSON file