settimeout | 易学教程

React Native cancel animation delay when component will unmount

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问题 I've a little problem with an animation. I try to do a Flash Bar Info on my app for the errors. So to do that I create a new component, this component can be place in one specific view or not, and when the error is trigger from my store the state of my component is change by componentWillReceiveProps and set to visible if there is an error message. So, if there isn't an error message my render function return false value but if there is an error message I run my render function with this

What is the random factor in node v10 event loop?

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问题 My question is about nodejs event loop Consider this code (async () => { let val = 1 const promise = new Promise(async resolve => { resolve() await new Promise(async r => { setTimeout(r) }) await promise val = 2 }) await promise await new Promise(resolve => setTimeout(resolve)) console.log(val) })() With node 10.20.1 (latest version of node 10) for ((i = 0; i < 30; i++)); do /opt/node-v10.20.1-linux-x64/bin/node race-timeout.js; done With node 12.0.0 (first version of node 12) for ((i = 0; i

Is there a faster way to yield to Javascript event loop than setTimeout(0)?

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问题 I am trying to write a web worker that performs an interruptible computation. The only way to do that (other than Worker.terminate() ) that I know is to periodically yield to the message loop so it can check if there are any new messages. For example this web worker calculates the sum of the integers from 0 to data , but if you send it a new message while the calculation is in progress it will cancel the calculation and start a new one. let currentTask = { cancelled: false, } onmessage =

Javascript, Promises and setTimeout

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问题 I have been playing with Promises, but I am having trouble understanding what is happening with the following code: const promise = new Promise((resolve, reject) => { console.log('Promise started - Async code started') setTimeout(() => { resolve('Success') }, 10) }) setTimeout(() => { console.log('Promise log inside first setTimeout') }, 0) promise.then(res => { console.log('Promise log after fulfilled') }) console.log('Promise made - Sync code terminated') setTimeout(() => { console.log(

Underscore debounce vs vanilla Javascript setTimeout

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问题 I understand that debounce in Undercore.js returns a function that will postpone its execution until the wait time is over. My question is, is there an advantage of using debounce over the regular setTimeout function in vanilla Javascript? Don't they both work the same? 回答1: They are very different and used in completely different cases. _.debounce returns a function , setTimeout returns an id which you can use to cancel the timeOut. No matter how many times you call the function which is

Underscore debounce vs vanilla Javascript setTimeout

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javascript setTimeout 0

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本文提供了一个 javascript 方面的 setTimeout 的一个例子，在执行长时间的堵塞任务时，相关页面渲染会有问题，直接提供代码，拿代码说例子是最简单的： <html> <script src= "js/jquery-1.10.2.min.js" type="text/javascript"></ script> <body> <button id= 'do'>Do long calc!</ button> <div id= 'status'></div > <div id= 'result'></div > <script type= "text/javascript"> jQuery( '#do').on( 'click', function(){ jQuery( '#status').text('calculating....' );//此处会触发redraw事件的fired，但会放到队列里执行，直到long()执行完。 // without set timeout, user will never see "calculating...." //long();//执行长时间任务，阻塞 // with set timeout, works as expected setTimeout( long,50);//用定时器，大约50ms以后执行长时间任务，放入执行队列

js中setTimeout的使用

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一、语法 setTimeout(code,millisec) code ：是含有 JavaScript 语句的字符串。这个语句可能诸如 "alert('5 seconds!')"，或者对函数的调用，诸如 alertMsg()。 millisec ：指示从当前起多少毫秒后执行第一个参数。二、setTimeout(code,millisec)中code包含形参的用法例如 var msg= 'dfdsf' ; setTimeout(alert(msg),1000); //alert(msg)会被立即执行 setTimeout(“alert(msg)”,1000);//系统报错解决办法是使用匿名函数回调 var msg='fewweeeee'; setTimeout(function(){alert(msg);},1000); 参考资料： js setTimeout http://www.studyofnet.com/news/916.html 来源： oschina 链接： https://my.oschina.net/u/2428791/blog/492859

[Javascript] 前端随笔

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做一个小功能时使用到的一点技术点记录下来： 1.在js中使用定时器：这两个方法都可以用来实现在一个固定时间段之后去执行JavaScript。不过两者各有各的应用场景。方法实际上，setTimeout和setInterval的语法相同。它们都有两个参数，一个是将要执行的代码字符串，还有一个是以毫秒为单位的时间间隔，当过了那个时间段之后就将执行那段代码。不过这两个函数还是有区别的，setInterval在执行完一次代码之后，经过了那个固定的时间间隔，它还会自动重复执行代码，而setTimeout只执行一次那段代码。虽然表面上看来setTimeout只能应用在on-off方式的动作上，不过可以通过创建一个函数循环重复调用setTimeout，以实现重复的操作： showTime(); function showTime() { var today = new Date(); alert( " The time is: " + today.toString()); setTimeout( " showTime() " , 5000 ); // 每隔5秒调用 showTime()，但是可以在函数中间中断 } 一旦调用了这个函数，那么就会每隔5秒钟就显示一次时间。 setInterval( " showTime() " , 5000 ); // 每隔5秒执行showTime()

细说setTimeout/setImmediate/process.nextTick的区别

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Node.js 中的非IO的异步API提供了四种方法，分别为setTimeOut(),setInterval(),setImmediate()以及process.nextTick()，四种方法实现原理相似，但达到的效果略有区别：一、事件循环Event Loop 首先，我们需要了解 node.js 的基于事件循环的事件模型，正是因为它才使得node. js 中回调函数十分普遍，也正是基于此，node.js实现了单线程高效的异步IO（这里说的单线程主要说的是执行 JavaScript 代码部分的线程，而异步IO部分node.js其实还是利用线程池去执行的）。简单的讲就是，在node.js启动时，创建了一个类似while(true)的循环体，每次执行一次循环体称为一次tick，每个tick的过程就是查看是否有事件等待处理，如果有，则取出事件极其相关的回调函数并执行，然后执行下一次tick。所以，有如下代码： A(); B(); C(); 1 2 3 1 2 3 它的执行逻辑是，先询问事件观察者当前是否有任务需要执行？观察者回答“有”，于是取出A执行，A是否有回调函数？如果有（如果没有则继续询问当前是否有任务需要执行），则取出回调函数并执行(注意：回调函数的执行基本都是异步的，可能不止一个回调)，执行完回调后通过某种方式通知调用者，我执行完了，并把执行结果给你，你自己酌情处理吧

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