问题
I'm trying to get the execution/response time of an asynchronous function that executes inside a node-fetch operation, like the following
async function getEditedData() {
var a = await fetch(`https://api.example.com/resorce_example`);
var b = await a.json();
// Some aditional treatment of the object obtained (b)
console.log("End of the asynchronous function")
}
I Used the library perf_hooks like this, but the execution time shows before
const hrtime = require ('perf_hooks').performance.now ;
var start = hrtime ();
getEditedData();
var end = hrtime ();
console.log (end - start);
I found the async_hooks library https://nodejs.org/api/perf_hooks.html#perf_hooks_measuring_the_duration_of_async_operations , but I can´t understand how it works. I am a basic in javascript/nodejs
回答1:
You could simply store Date.now() in some variable and then check Date.now()
when your Promise resolves (or rejects) and subtract to find the difference. For example:
const simulateSomeAsyncFunction = new Promise((resolve, reject) => {
console.log('Initiating some async process, please wait...')
const startTime = Date.now();
setTimeout(() => {
resolve(Date.now() - startTime);
}, 3000);
});
simulateSomeAsyncFunction.then(msElapsed => {
console.log(`Async function took ${msElapsed / 1000} seconds to complete.`);
});
Note: You could write code that achieves the same thing and appears to be synchronous by using await
/async
since that is just "syntactic sugar" built on top of Promises. For example:
const simulateSomeAsyncFunction = () => {
console.log('Initiating some async process, please wait...');
return new Promise((resolve, reject) => {
setTimeout(resolve, 3000);
});
};
// Await is required to be called within an async function so we have to wrap the calling code in an async IIFE
(async() => {
const startTime = Date.now();
await simulateSomeAsyncFunction();
const msElapsed = Date.now() - startTime;
console.log(`Async function took ${msElapsed / 1000} seconds to complete.`);
})();
回答2:
If you expect to set the end
after getEditedData()
is completed, you actually need to await getEditedData()
. Otherwise, you'll go right past it while it executes... asynchrnously.
回答3:
Starting with a simple async function -
const fakeAsync = async (value) => {
const delay = 2000 + Math.random() * 3000 // 2 - 5 seconds
return new Promise(r => setTimeout(r, delay, value))
}
fakeAsync("foo").then(console.log)
console.log("please wait...")
// "please wait..."
// "foo"
We could write a generic function, timeit
. This is a higher-order function that accepts a function as input and returns a new function as output. The new function operates like a decorated version of the original -
const timeit = (func = identity) => async (...args) => {
const t = Date.now()
const result = await func(...args)
return { duration: Date.now() - t, result }
}
// decorate the original
const timedFakeAsync = timeit(fakeAsync)
// call the decorated function
timedFakeAsync("hello").then(console.log)
timedFakeAsync("earth").then(console.log)
// { duration: 3614, result: "earth" }
// { duration: 4757, result: "hello" }
The timed version of our function returns an object, { duration, result }
, that reports the runtime of our async function and the result.
Expand the snippet below to verify the results in your own browser -
const identity = x =>
x
const timeit = (func = identity) => async (...args) => {
const t = Date.now()
const result = await func(...args)
return { duration: Date.now() - t, result }
}
const fakeAsync = async (value) => {
const delay = 2000 + Math.random() * 3000 // 2 - 5 seconds
return new Promise(r => setTimeout(r, delay, value))
}
const timedFakeAsync = timeit(fakeAsync)
timedFakeAsync("hello").then(console.log)
timedFakeAsync("earth").then(console.log)
console.log("please wait...")
// "please wait..."
// { duration: 3614, result: "earth" }
// { duration: 4757, result: "hello" }
来源:https://stackoverflow.com/questions/61018851/how-to-measure-the-execution-time-of-an-asynchronous-function-in-nodejs