types of consoles

The difference between null and undefined1. Types of differencesConsole.log (typeof (undefined));//undefinedConsole.log (typeof (null));//objectConsole.log (null==undefined);//trueConsole.log (null===undefined);//false------------extension, why Console.log (typeof (null));//object-----This is because ES is designed to assume that null represents an empty object pointer, except that the value is empty, but the code executes properly. So when using type

JavaScript variable type Value types: String, numeric, Boolean, Null, Undefined Reference types: Arrays, objects, functions Comparison of value type and reference type Compare these two types through two instances (Debug environment: Chrome Developer Tool Console) Value type instance var a = ' Hello ';var B = A;b /* Hello * *A = ' world ';b /* Hello * * Th

Strongly typed and weakly typedIf a language rarely has an implicit conversion type, it means that he is a strongly-typed language. If you do this often, it means that he is a weakly typed language. Java, C + +, and Python are strongly typed languages. Php,javascript and Perl are weakly typed languagesstatic types and dynamic typesThe language at compile-time check type is a static type language, and the language of the check type at run time is a dyn

SQL data Type JDBC Type Code standard Java type types of Java extensions for Oracle 1.0 Standard JDBC Type: CHAR java.sql.Types.CHAR java.lang.String oracle.sql.CHAR VARCHAR2 java.sql.Types.VARCHAR java.lang.String oracle.sql.CHAR LONG java.sql.Types.LONGVARCHAR java.lang.String oracle.sql.CHAR NUMB

Tags: file type common file system typeSeven types of files common in Linux:-Normal fileD catalog FileL link file (point to another file, similar to its shortcut)s socket fileB-block device files, binary filesC-Character device filesP Named pipe file Linux common File system types:EXT4 Linux File systemSwap Linux Swap partitionsISO9660 CD-ROM file systemVFAT a generic term for the fat (including FAT16 and Fat32) file systems under Windows systemsA f

Date type Storage space Date format Date Range Datetime 8 bytes YYYY-MM-DD HH:MM:SS 1000-01-01 00:00:00 ~ 9999-12-31 23:59:59 Timestamp 4 bytes YYYY-MM-DD HH:MM:SS 1970-01-01 00:00:01 ~ 2038 Date 3 bytes Yyyy-mm-dd 1000-01-01 ~ 9999-12-31 Year 1 bytes YYYY 1901 ~ 2155 A column of the timestamp type has an attribute: By default, when the INSERT, update

Four types of relationships in UML and four types of UML 1. Association Description: Assocition: Describes the structural relationship between two or more classes. (1) Common Association: 1) Association name: used to describe the nature of the link. 2) Role: When a class is at one end of the Association, the class plays a specific Role in the relationship; A role is the responsibility of a class close to on

used escape symbols, such as:650) this.width=650; "Src=" Http://s5.51cto.com/wyfs02/M00/85/A9/wKioL1er28Sj-6f1AABTU_efbug631.png-wh_500x0-wm_3 -wmp_4-s_3537525234.png "title=" 12.png "alt=" Wkiol1er28sj-6f1aabtu_efbug631.png-wh_50 "/>In addition to the use of the transfer, we can actually use "" "(three double quotes) or" (three single quotation marks) (this is actually mentioned in the python quotation marks when we mention it), so that the escape character such as line break does not need to

There are three ways to convert a base type to a string:1. Use the ToString () method of the wrapper class2. Using the ValueOf () method of the String class3. Using an empty string with the base type, you get the string that corresponds to the base type dataint c=10;String str1=integer.tostring (c); Method OneString str1=string.valueof (c); Method TwoString str=c + ""; Method ThreeThere are two ways to convert a string into a basic type:1. Call the Parasexxx static method of the wrapper class2.

Seven types of join in MySQL and seven types of join in mysqlCreate a table Here we will first create two tables with foreign key associations. Create database db0206; USE db0206; create table 'db0206 '. 'tbl _ dept' ('id' INT (11) not null AUTO_INCREMENT, 'deptname' VARCHAR (30), 'locadd' VARCHAR (40 ), primary key ('id') ENGINE = innodb charset = utf8; create table 'db0206 '. 'tbl _ emp' ('id' INT (11) no

Basic Data Types in JAVA, JAVA Data Types Byte: The smallest data type in java.1 byte/8 bits. -128 (2 ^ 7 )~ 127 (2 ^ 7-1), default value 0. Short: short integer,2 bytes/16 bits, range:-32768 (-- 2 ^ 15 )~ 32767 (2 ^ 15-1), default value 0 Int: integer,4 bytes/32 bits, value range:-2147483648 (-2 ^ 31 )~ 2147483647 (2 ^ 31-1), default value 0 Long: long integer,8 bytes/64-bit,-2 ^ 63 (-2 ^ 63 )~ 2 ^ 63-

Using system;using system.collections.generic;using system.linq;using system.text;namespace P01Method{class Program {static void Main (string[] args) {//int A1 = 11; int b2 = 22; Add2num (A1, B2);//When invoking a method, the value passed in the method's parentheses is called the argument (actual parameter)//add2num (102, 205), or, in the method of invocation, it is possible to pass a value directly to the parameter int res = Add2numwith (222, 555);//U

Null: Empty, indicating that the yield does not point to any object,such as: string = null;int a = null;//is wrongBut you can do this by adding a question mark after the type.Int? A = null;//This is right and is a special type of intint B = 12;Cannot convert directly to int after adding a question markint B = a;//this is wrong.int b = (int) a;//is correct after coercion type conversion, but must be guaranteedA is not NULLSummary: Not an empty data type, followed by a question mark can be null,Bu

Introduction to classes and types in python and introduction to python types What is a class? It can be regarded as a synonym of type or type. All objects belong to a class called a class instance. For example, birds are "Birds" instances. This is a general (abstract) class with many sub-classes: the bird you see may belong to the sub-class "lark ". You can think of "Birds" as a collection of all birds, and

Two types of thread implementation and thread alternate execution, two types of thread alternate execution I learned a lot about the thread. record it. I. Two main implementation methods of threads. 1. inherit the Thread class and override the run () method. Create a subclass in the main method and call the start () method. Example: // Inherit the Thread class and override the run () method Public class Thr

MicrosoftAccess provides two field data types (Field Data Type: determines which data field features can be stored. For example, text fields can store data consisting of text or numeric characters, while numeric fields can only store numerical data .) To store text or numbers, or a combination of the two: Text and remarks. Microsoft Access provides two field data types (Field Data Type: determines which dat

There are two main ways to convert between the two, the first is that the built-in type is converted to a user-defined type, where an int type is converted to an object of class type, and the second is a class-type conversion to an int typeThe former relies on the conversion constructor, which relies on the custom type conversion functionI. Conversion constructorsTwo. Type conversion constructors#include Cross-conversion of built-in types and user-def

9 different types of breadcrumb and distributed multi-step navigation, 9 types of Navigation [Commonly used bread chips] 9 different bread chips and distributed multi-step navigation Instance code 　　 Run

little bit of precision, regardless of how many of the mantissa can be accurately represented by the binary used internally. This can result in confusion: for example, floor ((0.1+0.7) *10 typically returns 7 instead of 8 as expected because the internal representation of the result is actually similar to 7.9999999999999991118 .... So never believe that the floating-point number is accurate to the last one, and never compare two floating-point numbers for equality. This article introduces the i

Python variables and types, Python variable types1. The program is used to process data, and the variable is used to store data. Number1 = 1002. to make full use of the memory space and manage the memory more efficiently, variables have different types. 3. How do I know the type of a variable? 3.1 In python, as long as a variable is defined and has data, the type of the variable has been determined. Deve