如何在循环内的 javascript 中创建 waitFor(delay) 函数？

Question

我正在尝试在 Node.js 中的循环内添加延迟。我有一个数组，需要为数组的每个元素调用一个函数。问题是每个这样的函数调用都应该有 30 秒的间隔。这是我尝试过的 -

const cprRedshift = async (page) => {
    let query = "select links from schema.table", links = [], ranks = []
    let data = await redshiftSelect(query)
    data.rows.forEach(element => {
        links.push(element.links)
    })

    let hostnames = await getDomainNames(links)

    // one way
    for(let i = 0; i < hostnames.length; i++){
            await setTimeout(async () => await checkPageRank(hostnames[i]), 30000)
    }

    // another way    
    let i = 0
    while(i < hostnames.length){
        await checkPageRank(page, hostnames[i])
        setInterval(() => ++i, 30000)
    }
}

checkPageRank 是同一脚本中的一个函数，我需要为 hostnames[] 数组中的所有元素调用它，同时在每次调用之间保持 30 秒的间隔。任何关于如何实现这一目标的想法将不胜感激。谢谢！

Answer 1

这是执行此类操作的常见模式的简化示例：

const hostnames = ["one", "two", "three", "four", "five", "six"];

function go (index = 0) {
  // do whatever you need to do for the current index.
  console.log(hostnames[index]);
  
  // if we haven't reached the end set a timeout
  // to call this function again with the next index.
  if (hostnames.length > index + 1) {
    setTimeout(() => go(index + 1), 1000);
  }
}

// kick it off
go();

Answer 2

您可以使用

let aWait=(x)=>new Promise((resolve)=>setTimeout(resolve,x));

然后将循环重写为

 for(let i = 0; i < hostnames.length; i++){
            await checkPageRank(hostnames[i]);
            await aWait(30000);
    }

Answer 3

的变体可能包括传递和使用数组本身，而不是递增计数器：

const hostnames = ["one", "two", "three", "four", "five", "six"];

function go ([current, ...remaining]) {
  // do whatever you need to do for the current item.
  console.log(current);
  
  // if there are items remaining, set a timeout to
  // call this function again with the remaining items
  if (remaining.length) {
    setTimeout(() => go(remaining), 1000);
  }
}

// kick it off
go(hostnames);

如何在循环内的 javascript 中创建 waitFor(delay) 函数？

How can i make a waitFor(delay) function in javascript inside a loop?

javascript

settimeout

node.js