type binary-foramt: use binary encoding, 使用某种二进制格式表示数据 text-format: use character encoding, 使用字符表示数据
binary format:
less space， compactly 不需要冗余的符号 key可以代替 text-foramt:
human-readable character-encoding:
ascii uft-16 uft-18 uft-16 1 2 3 4 5 6 POST /api/endpoint HTTP/1.1 Host: example.com Content-Type: application/json; charset=utf-16 Content-Length: 34 {"name":"John Doe","age":30} other encode; serilization 关系； same: one format -> another format; differ: serialization is a specific instace
econde: one format -> any format; serilization: any -> array of bytes binary-format vs textual-format; json: “{“number”: 1}”
makefiletutorial what-how-makefile A Good Makefile for Go
what makefile do main purpose: comiple c,c++ file into a binary file; other purpose: combine a serious of task into a specific task; syntax 1 2 3 4 Do: requisite1, requisite2... task1; task2; task3; Do: the target file OR the action Name requisite: the dependent files; task
1 2 3 4 hello: hello.go build hello.go -o hello hello.go: echo "println("hello")" > hello.go PHONEY makefile task won’t excute every time, it will check target file and source file;
Order of execution of a Query
overview DQL: date query DDL: data definition; action: create drop alter truncate; object: table index database; event; view trigger DML: update/delete/insert DCL: data control grant revoke sql write order 1 2 3 4 5 6 7 8 SELECT DISTINCT column, AGG_FUNC(column or expression) FROM table JOIN anotherTable WHERE constraint_expression GROUP BY column HAVING constraint_expression ORDER BY column ASC/DESC LIMIT count OFFSET count; run order FROM/JOIN clause: determine the total data set; WHERE clause: GROUP BY clause HAVING clause SELECT clause DISTINCT ORDER BY clause 1.
Cross-domain Ajax with Cross-Origin Resource Sharing
cors cross-origin resource sharing
cors is an http based meachamism that allow a server to indicate that any other origin
cors is a w3c draft define how the brower and the server communicate when accessing resource origin;
how to do? 1. simple request 1. requirements One of the allowed methods:GET;HEAD;POST the only headers which are allowed to be manually set are Accept Accept-Language Content-Language Content-Type (but note the additional requirements below) The only allowed values for the Content-Type header are: application/x-www-form-urlencoded multipart/form-data text/plain 2.
life cycle
life cycle constructor() static getDerivedStateFromProps() is invoked before calling the render methods, both on the initial mount and on subsequent updates
render() componentDidMount() hook add state, fetch and other features to the react function component
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 import React, { useState } from 'react'; function Example() { // Declare a new state variable, which we'll call "count" const [count, setCount] = useState(0); return ( <div> <p>You clicked {count} times</p> <button onClick={() => setCount(count + 1)}> Click me </button> </div> ); } Equivalent class;
是什么? 代表 被忽略的变量 underscore means ignoring the value;
use case 多个返回值忽略错误值 1 2 3 4 5 if _, isExists := ageMaps["jim"];isExists{ // do other thing } 引入副作用(side effects) the import package is ignored, but the init function have taken effect;
1 2 3 4 5 6 7 import ( _ "github.com/go-sql-driver/mysql" ) func init() { sql.Register("mysql", &MySQLDriver{}) } 检测是否实现接口 1 var _ DogType = (*BullDog)(nil)
