Javascript Intermediate Grammar Quick Start

  • 2021-07-06 10:01:32
  • OfStack

1. Talk about the object of Javascript

Javascript is not only a weak language type, but also a dynamic language type. In the process of using Javascript, it is often necessary to use the built-in objects and custom objects of Javascript.

1.1 How to Create an Object
Javascript is a weak language type language, so it is not necessary to create objects by constructor like Java, C # and other high-level languages. In Javascript, there are mainly two methods to create objects, one is defined directly by new keywords, and the other is defined by functions. As follows:

  // No. 1 1 In a way, directly through new Create an object; 
  var demo = new Object(); = "Anderson"; = "male";
  demo.age = 23;

  // No. 1 2 Format, direct instantiation , Basically and Json The grammar is 1 As a result, 1 General as the first 1 Alternative grammar in a variety of ways. 
  var demo = {name:"Anderson",sex:"male",age:25};

  // No. 1 3 Format, create objects through constructors 
  function Demo(name,sex,age){ = name; = sex;
    this.age = age;
  var demo = new Demo("Andeson","male",25);

1.2 How to Modify Objects

The object syntax of Javascript and high-level language is different. Generally speaking, its limitation is less. After creating an object, you can dynamically modify the attributes and methods of the object, such as adding a new attribute and adding a new method.

  var demo = {Name:"Anderson"} ; 
  demo.Sex = "male";

1.3 Understanding Digital Objects in Javascript

In Javascript, all numbers are 64 bits, and all numbers are composed of floating-point types. Javascript uses the 64-bit floating-point format defined by IEEE 754 standard to represent numbers, which can represent a maximum value of 1.7976931348623157 x 10308 and a minimum value of 5 x 10-324.

  var demo1 = 7;    //10 Binary notation 
  var demo2 = 07;   //8 Binary notation 
  var demo3 = 0x12;  //106 Binary notation 

  var demo4 = 12e12;  // Scientific notation 
  var demo5 = 12e-12; // Scientific notation 

  var demo7 = 128;
  var demo8 = demo7.toString(16); // Convert to 106 Binary system 
  var demo9 = demo7.toString(8);  // Convert to 8 Binary system 
  var demo10= demo7.toString(2);  // Convert to 2 Binary system 

  var demo11= Infinity;   // Infinity representation 
  var demo12= isNaN(100);  // Non-numerical value representation 

  var demo13= typeof(12);       // The type of the number is  Number
  var demo14= typeof(new Number(12)); //Number The type of is Object
  var demo15 = (demo13 == demo14);   // The two are equal 
  var demo16 = (demo13=== demo14);   // The two are not equal 

1.4 Understanding String Objects in Javascript

  var str = "Hello,Anderson";

  var demo1 = str[0];        // Get the characters in the string by index , Returns if the maximum value is exceeded undefined
  var demo2 = str.indexOf("H");   // Gets the position of the target string in the source string, and returns if it cannot be found  -1
  var demo3 = str.length;      // Gets the length of the string 
  var demo4 = str.lastIndexOf("H"); // Gets the position of the target string in the source string, starting from the end of the string, and can't find it. Return -1
  var demo5 = str.match("Anderson");// Match the target string from the source string, if yes, return the target string, otherwise, return  null
  var demo8 = str.replace("A","d"); // Replace the target string in the source string with a replacement string 
  var demo9 = str.toUpperCase();  // Convert to uppercase 
  var demo10= str.toLowerCase();  // Convert to lowercase 
  var demo11= str.split("d");    // Convert to an array 

  var demo12= "\'";    // Indicates single quotation marks 
  var demo13= "\"";    // Represents double quotation marks 
  var demo14= "\\";    // Represents a slash 
  var demo15= "\n";    // Indicates a line break 
  var demo16= "\r";    // Indicates carriage return 
  var demo17= "\t";    // Representing tabs 
  var demo18= "\b";    // Represents a space 
  var demo19= "\f";    // Represents page change 

1.5 Understanding Date Objects in Javascript

  var demo1 = new Date();      // Create object, current date 
  var demo2 = new Date(22e9);    // Create object, milliseconds 
  var demo3 = new Date("2016-06-04");// Create object, date string 
  var demo4 = new Date(2016,5,12,12,12,12); // Create object, year, month, day, hour, second 

  var demo5 = (demo1 > demo2);    // Comparison date 

1.6 Understanding Array Objects in Javascript

  var demo1 = new Array(1,2,3,4);    // Create an array 
  var demo2 = [1,3,4,5];        // Create an array 
  var demo3 = demo1.concat(demo2);   // Merge array 
  var demo5 = demo1.concat(demo2,demo3);// Merge array 

1.7 Understanding the regular object RegExp in Javascript

RegExp is the abbreviation of Regular Expression (Regular Expression). Regular expressions are mainly used for text retrieval. Its basic grammatical form is as follows:

  var pattern = new RegExp(pattern,modifiers); // Creating regular objects through constructors 
  var pattern = /pattern/modifiers;       // Declare regular objects directly 

  // Where the modifier modifiers There are two kinds, i And g , i Indicates case insensitivity, g Represents full-text retrieval 
  //pattern Representation retrieval model 

  var str = "Hello, Anderson Lu" ; 
  var pattern = /llo/gi;
  var demo1 = str.match(pattern); // Use instances 

  var pattern2 = new RegExp("\\Lu\\gi");
  var demo2 = pattern2.test(str); // Judge str Is there a conformance pattern in pattern2 Returns the string of true Or false
  var demo3 = pattern2.exec(str); // Returns a matching string 

Ok, this is the end of the article. Besides, there are 1 other objects, such as Math arithmetic and Boolean. You can learn through this site.

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