每 2 秒获取一次调用，但不希望请求堆积

Fetch call every 2 seconds, but don#39;t want requests to stack up(每 2 秒获取一次调用，但不希望请求堆积)

问题描述

我正在尝试进行 API 调用，我希望它每 2 秒重复一次.但是我担心如果系统在 2 秒内没有收到请求，它会建立请求并继续尝试发送它们.我怎样才能防止这种情况发生?

I am trying to make an API call and I want it to repeat every 2 seconds. However I am afraid that if the system doesn't get a request back in 2 seconds, that it will build up requests and keep trying to send them. How can I prevent this?

这是我尝试获取的操作:

const getMachineAction = async () => {
    try {
        const response = await fetch( 'https://localhost:55620/api/machine/');
        if (response.status === 200) {
            console.log("Machine successfully found.");
            const myJson = await response.json(); //extract JSON from the http response
            console.log(myJson);               
        } else {
            console.log("not a 200");
        }
    } catch (err) {
        // catches errors both in fetch and response.json
        console.log(err);
    }
};

然后我用 setInterval 调用它.

function ping() {
    setInterval(
        getMachineAction(),
        2000
    );        
}

我曾想过在 setInterval 中做一些类似结构的承诺，以确保获取已经工作并完成，但无法使其正常工作.

I have thought of doing some promise like structure in the setInterval to make sure that the fetch had worked and completed, but couldn't get it working.

推荐答案

Promise.all() 解决方案

此解决方案可确保您不会错过 2 秒延迟要求，也不会在另一个网络呼叫正在进行时触发呼叫.

This solution ensures that you don't miss-out on 2 sec delay requirement AND also don't fire a call when another network call is underway.

function callme(){
//This promise will resolve when the network call succeeds
//Feel free to make a REST fetch using promises and assign it to networkPromise
var networkPromise = fetch('https://jsonplaceholder.typicode.com/todos/1');


//This promise will resolve when 2 seconds have passed
var timeOutPromise = new Promise(function(resolve, reject) {
  // 2 Second delay
  setTimeout(resolve, 2000, 'Timeout Done');
});

Promise.all(
[networkPromise, timeOutPromise]).then(function(values) {
  console.log("Atleast 2 secs + TTL (Network/server)");
  //Repeat
  callme();
});
}
callme();

注意:这会按照问题作者的要求处理不良案例定义:

Note: This takes care of the bad case definition as requested by the author of the question:

坏情况"(即需要超过 2 秒)是我希望它跳过该请求，然后发送一个新请求.所以在 0 秒时请求发送.需要 3 秒执行，然后 2 秒后(在 5)它应该重新执行.所以它只是延长时间直到它发送."

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