下面这个函数并没有像我想要的那样工作;作为一个JS新手，我不明白为什么。
我需要它等待5秒，然后检查newState是否为-1。
目前，它不会等待，它只是直接检查。
function stateChange(newState) {
setTimeout('', 5000);
if(newState == -1) {
alert('VIDEO HAS STOPPED');
}
}
当前回答
你必须把你的代码放在你提供给setTimeout的回调函数中:
function stateChange(newState) {
setTimeout(function () {
if (newState == -1) {
alert('VIDEO HAS STOPPED');
}
}, 5000);
}
任何其他代码将立即执行。
其他回答
您可以通过对函数(async和await)进行一些小更改来增加延迟。
const addNSecondsDelay = (n) => {
return new Promise(resolve => {
setTimeout(() => {
resolve();
}, n * 1000);
});
}
const asyncFunctionCall = async () {
console.log("stpe-1");
await addNSecondsDelay(5);
console.log("step-2 after 5 seconds delay");
}
asyncFunctionCall();
您真的不应该这样做，正确使用timeout是解决OP问题的正确工具，以及任何其他您只想在一段时间后运行某些内容的情况。约瑟夫·西尔伯在他的回答中很好地证明了这一点。然而，如果在一些非生产的情况下，你真的想挂起主线程一段时间，这将做到这一点。
function wait(ms){
var start = new Date().getTime();
var end = start;
while(end < start + ms) {
end = new Date().getTime();
}
}
以以下形式执行:
console.log('before');
wait(7000); //7 seconds in milliseconds
console.log('after');
I've arrived here because I was building a simple test case for sequencing a mix of asynchronous operations around long-running blocking operations (i.e. expensive DOM manipulation) and this is my simulated blocking operation. It suits that job fine, so I thought I post it for anyone else who arrives here with a similar use case. Even so, it's creating a Date() object in a while loop, which might very overwhelm the GC if it runs long enough. But I can't emphasize enough, this is only suitable for testing, for building any actual functionality you should refer to Joseph Silber's answer.
创建这样一个以毫秒为单位等待的函数的最好方法是，这个函数将在参数中提供的毫秒内等待:
函数waitSeconds(imillisecseconds) { Var计数器= 0 ， start = new Date().getTime() ， end = 0; while (counter < imillisecseconds) { end = new Date().getTime(); Counter = end - start; ｝ ｝
试试这个:
//the code will execute in 1 3 5 7 9 seconds later
function exec() {
for(var i=0;i<5;i++) {
setTimeout(function() {
console.log(new Date()); //It's you code
},(i+i+1)*1000);
}
}
如果你在一个异步函数中，你可以简单地在一行中完成:
console.log(1);
await new Promise(resolve => setTimeout(resolve, 3000)); // 3 sec
console.log(2);
供你参考，如果目标是NodeJS，你可以使用这个内置函数(这是一个预定义的setTimeout函数):
import { setTimeout } from 'timers/promises';
await setTimeout(3000); // 3 sec
