async function & async callback js & ES7 & promise

async-function-async-callback-js.md

async function & async callback js & ES7

https://caolan.github.io/async/docs.html

https://caolan.github.io/async/

https://github.com/caolan/async

async function & promise

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Statements/async_function

async function 声明定义了一个异步函数，它返回一个 AsyncFunction 对象。

你还可以定义异步函数, 使用一个 async function expression 。

function resolveAfter2Seconds(x) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(x);
    }, 2000);
  });
}

async function add1(x) {
  var a = resolveAfter2Seconds(20);
  var b = resolveAfter2Seconds(30);
  return x + await a + await b;
}

add1(10).then(v => {
  console.log(v);  // prints 60 after 2 seconds.
});

async function add2(x) {
  var a = await resolveAfter2Seconds(20);
  var b = await resolveAfter2Seconds(30);
  return x + a + b;
}

add2(10).then(v => {
  console.log(v);  // prints 60 after 4 seconds.
});

通过异步方法重写 promise 链

function getProcessedData(url) {
  return downloadData(url) // returns a promise
    .catch(e => {
      return downloadFallbackData(url) // returns a promise
    })
    .then(v => {
      return processDataInWorker(v); // returns a promise
    });
}


// equal to 


async function getProcessedData(url) {
  let v:
  try {
    v = await downloadData(url); 
  } catch (e) {
    v = await downloadFallbackData(url);
  }
  return processDataInWorker(v);
}

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/await

promise

https://www.promisejs.org/

https://promisesaplus.com/

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Promise

https://developers.google.com/web/fundamentals/getting-started/primers/promises?hl=zh-cn

https://api.jquery.com/promise/

http://exploringjs.com/es6/ch_promises.html

https://medium.com/javascript-scene/master-the-javascript-interview-what-is-a-promise-27fc71e77261

Asynchronous programming in Node.js

https://blog.risingstack.com/node-js-async-best-practices-avoiding-callback-hell-node-js-at-scale/

Callback Hell

http://callbackhell.com/

fs.readdir(source, function (err, files) {
  if (err) {
    console.log('Error finding files: ' + err)
  } else {
    files.forEach(function (filename, fileIndex) {
      console.log(filename)
      gm(source + filename).size(function (err, values) {
        if (err) {
          console.log('Error identifying file size: ' + err)
        } else {
          console.log(filename + ' : ' + values)
          aspect = (values.width / values.height)
          widths.forEach(function (width, widthIndex) {
            height = Math.round(width / aspect)
            console.log('resizing ' + filename + 'to ' + height + 'x' + height)
            this.resize(width, height).write(dest + 'w' + width + '_' + filename, function(err) {
              if (err) console.log('Error writing file: ' + err)
            })
          }.bind(this))
        }
      })
    })
  }
})

Object.getPrototypeOf()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/GetPrototypeOf

Object.getPrototypeOf() 方法返回指定对象的原型（即, 内部[[Prototype]]属性的值）。

object 要返回其原型的对象。
给定的对象的原型。如果没有继承的属性，则返回 null 。

在 ES5 中，如果参数不是一个对象类型，将抛出一个 TypeError 异常。在 ES6 中，参数被强制转换为Object。

Object.getPrototypeOf(window);

// Window {TEMPORARY: 0, PERSISTENT: 1, Symbol(Symbol.toStringTag): "Window", constructor: function}


let proto = {};

proto.name = "xgqfrms";

let obj = Object.create(proto);

Object.getPrototypeOf(obj) === proto;
 // true

Object.prototype.isPrototypeOf()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/isPrototypeOf

isPrototypeOf() 方法用于测试一个对象是否存在于另一个对象的原型链上。

Note: isPrototypeOf() 与 instanceof 运算符不同。
在表达式 "object instanceof AFunction"中，对象原型链是针对 AFunction.prototype 进行检查的，而不是针对 AFunction 本身。

handler.getPrototypeOf()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Proxy/handler/getPrototypeOf

handler.getPrototypeOf() 是一个代理方法，当读取代理对象的原型时，该方法就会被调用。

Object.setPrototypeOf()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/setPrototypeOf

Object.setPrototypeOf() 方法设置一个指定的对象的原型 ( 即, 内部[[Prototype]]属性）到另一个对象或 null。

Object.prototype.__proto__

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/proto

Object.prototype 的 proto 属性是一个访问器属性（一个getter函数和一个setter函数）, 暴露了通过它访问的对象的内部[[Prototype]] (一个对象或 null)。

Object.setPrototypeOf = Object.setPrototypeOf || function (obj, proto) {
  obj.__proto__ = proto;
  return obj; 
}

handler.get()

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Proxy/handler/get

handler.get() 方法用于拦截对象的读取属性操作。

Object.getPrototypeOf()

Object.getPrototypeOf()

es6-summary

https://gist.github.com/xgqfrms-GitHub/701beb8426abb2275ce0d758bc294404

Node.js Async Best Practices & Avoiding the Callback Hell

https://blog.risingstack.com/node-js-async-best-practices-avoiding-callback-hell-node-js-at-scale/

CORS & CSP

fetch & jsonp

https://gist.github.com/xgqfrms-GitHub/840fe27cecb9e7217fb4f0b09db19406