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轻松使用WebWorker,解放耗时较大的算法代码

Web Worker为Web内容在后台线程中运行脚本提供了一种简单的方法。线程可以执行任务而不干扰用户界面。

基础知识

MDN 讲解的已经较详细,此处不再重复。

常规用法

main.js

var first = document.querySelector('#number1');
var second = document.querySelector('#number2');
var result = document.querySelector('.result');
if (window.Worker) { // Check if Browser supports the Worker api.
// Requires script name as input
var myWorker = new Worker("worker.js");
// onkeyup could be used instead of onchange if you wanted to update the answer every time
// an entered value is changed, and you don't want to have to unfocus the field to update its .value
first.onchange = function() {
myWorker.postMessage([first.value,second.value]); // Sending message as an array to the worker
console.log('Message posted to worker');
};
second.onchange = function() {
myWorker.postMessage([first.value,second.value]);
console.log('Message posted to worker');
};
myWorker.onmessage = function(e) {
result.textContent = e.data;
console.log('Message received from worker');
};
}

worker.js

onmessage = function(e) {
console.log('Message received from main script');
var workerResult = 'Result: ' + (e.data[0] * e.data[1]);
console.log('Posting message back to main script');
postMessage(workerResult);
}

巧妙用法

通过使用封装好的WebWorker类和整理后的worker.js:
  1. 1.
    简化了对Worker类的调用;
  2. 2.
    无需进一步修改worker.js内部方法;
  3. 3.
    可以执行在任意脚本文件中的方法,无需copy到worker.js文件中;

WebWorker类

WebWorker.js
// 封装了一个WebWorker类
class WebWorker {
constructor(options)
{
if (window.Worker && options.workerUrl)
{
this.worker = new Worker(options.workerUrl);
this.onMessage();
this.onError(options && options.errorCallback);
}
else
{
alert('Browser does not support Worker, or workerUrl not set!');
}
}
static getInstance(options)
{
if (!this.instance)
{
this.instance = new WebWorker(options);
}
return this.instance;
}
onMessage()
{
this.worker.onmessage = function (e) {
if (e.data)
{
let {result, callback} = e.data;
call(callback, result);
}
else
{
alert(`onmessage error: ${e}!`);
}
// throw new Error('Something wrong!'); // onerror
};
}
postMessage(method = null, params = [], callback = null, scripts = [], isClose = false)
{
scripts = Array.isArray(scripts) ? scripts : [scripts];
this.worker.postMessage({method, params, callback, scripts});
}
onError(errorCallback)
{
this.worker.onerror = function (err) {
console.table(err);
errorCallback && errorCallback(err);
};
}
terminate()
{
this.worker.terminate();
}
}
/**
* A funtcion which can easily invoke function from a string method name
* @param method, eg: 'alert', 'math.floor', 'math.floor.toString'
* @param params
* @return {Promise<any>}
*/
const call = (method, params) => {
let callMethod = (callers, thisArg) => {
let caller = callers.shift();
thisArg = thisArg || window;
thisArg = thisArg[caller];
if (callers.length > 0)
{
thisArg = callMethod(callers, thisArg);
}
return thisArg;
};
return new Promise((resolve) => {
let callers = method.split('.');
params = Array.isArray(params) ? params : [params];
let result = callMethod(callers)(...params);
resolve(result);
});
};

math.js: 耗时大,且会阻塞线程影响浏览器渲染的方法

function isPrime (number) => {
if (number === 0 || number === 1)
{
return true;
}
for (let i = 2; i <= Math.sqrt(number); i++)
{
if (number % i === 0)
{
return false;
}
}
return true;
};

worker.js: 一个专用worker仅仅能被生成它的脚本所使用。

const call = (method, params) => {
let callMethod = (callers, thisArg) => {
let caller = callers.shift();
thisArg = (thisArg ? thisArg : this)[caller];
if (callers.length > 0)
{
thisArg = callMethod(callers, thisArg);
}
return thisArg;
};
return new Promise((resolve) => {
let callers = method.split('.');
params = Array.isArray(params) ? params : [params];
let result = callMethod(callers)(...params);
resolve(result);
});
};
const applyMethod = (data) => {
let {method, params, scripts} = data;
scripts && importScripts.apply(this, scripts);
return call(method, params);
};
// WebWorker
onmessage = function (e) {
let {method, params, scripts, callback, isClose} = e.data;
applyMethod({method, params, scripts})
.then((result) => {
postMessage({result: result, callback: callback});
isClose && close();
});
};

main.js: 引入到页面,初始化WebWorker

const options = {
workerUrl: window.location.origin + '/worker.js'
};
// postMessage(methodName, params, callbackName, scripts, isClose);
WebWorker.getInstance(options).postMessage('isPrime', '1000001111111111', 'console.log', [window.location.origin + '/math.js']);
通过main.js的调用方法,可以使任意文件的方法被调用。

使用注意:

  1. 1.
    workerUrl: 使用绝对地址或者相对WebWorker.js的地址(Worker是在WebWorker中初始化的);
  2. 2.
    scripts: 被引入的script文件必须是传统JS库;
“依赖传统JS库”意为着被依赖的JS文件,很有可能不是 CMD,AMD,UMD或ES 6模块文件。相反,所谓的传统JS库文件通常是被包装成为一个IIFE表达式(即,一个立即执行的大闭包),并且输出一个全局变量作为暴露API集的顶层命名空间。