How to run the same promises one after another NodeJs
I am trying to solve the following problem. Consider the following case. I need to check if an array of servers is alive. Or, to be more specific, I need to find the first working server from the list provided, I need to do this one by one.
For example, if the first server is down, check the other and the other ...
Since NodeJS is asynchronous, I cannot do this in a for loop. So I tried to implement something similar to recursion, it looks ugly and doesn't work, but I tried)
static findWorkingServer(servers, payload) {
return NetworkUtils.getMyPublicIP()
.then((ip) => {
return new Promise(function (resolve, reject) {
let currentIndex = -1;
if (servers.length > 0) {
let currentServer;
let serverCheckCallback = function (result) {
if (result) {
resolve({working: currentServer, payload: payload});
}
else {
if (currentIndex < servers.length-1) {
currentIndex++;
currentServer = servers[currentIndex];
NetworkUtils.checkIfServerWorking(currentServer, ip)
.then(serverCheckCallback);
}
else {
reject(new Error("No working servers found"))
}
}
};
serverCheckCallback(false);
}
else {
resolve(new Error("No servers provided"));
}
})
});
}
static checkIfServerWorking(credentials, publicIp) {
return new Promise(function (resolve, reject) {
if(credentials) {
request({
url: credentials.url,
agentClass: agentClass,
agentOptions: {
// Agent credentials
}
})
.then(res => {
// Do some stuff with resposne
resolve(someCondition);
})
.catch(err => {
resolve(false);
});
}else {
resolve(false);
}
});
}
Please help to get the desired result, maybe it is possible to run queries synchronously.
+3
source to share
1 answer
Can be done with await / async:
let servers = ["test0.com","test1.com","test2.com","test3.com","test4.com"]
class ServerTest {
static async checkServer(name) {
if (name === "test3.com")
return true //returns promise that resolves with true
else
return false //returns promise that resolves with false
}
}
(async()=>{ //IIFE (await can only be used in async functions)
let targetServer
for (i in servers) {
if (await ServerTest.checkServer(servers[i]) === true) {
targetServer = servers[i]
break
}
}
console.log("Found a working server: " + targetServer)
})()
+1
source to share