I am not an experienced Javascript programmer but I find it very difficult to execute 2 time-consuming functions in the row.
I have spent some days on studying promises or async/await but not success so far.
console.log("synch 1");
slowFunction1();
slowFunction2();
console.log("synch 2");
Most examples describe get json functions,setTimeOut etc. But in my case I have to do heavy mathematical calculations and the sequential execution is required. How could I do this?
Depends on what you're trying to achieve and what the environment is. I will assume the slow function is blocking and you're going for the main thread not to be blocked during execution. Assuming you are talking about:
Some example code would be:
var myWorker = new Worker('file-containing-slow-code.js');
myWorker.postMessage({execute: 'slowFunction1'});
myWorker.onmessage((msg) => {
const {result, functionExecuted} = msg.data;
console.log(result);
});
//contents of file-containing-slow-code.js
onmessage = function(e) {
var result = funcs[e.data.execute]();
postMessage({result, functionExecuted: e.data.execute});
}
const funcs = {
slowFunction1: () => {
// do slow stuff;
}
};
You could wrap your functions in a promise like this, and only resolve when you want the code to continue:
function slowFunction1() {
return new Promise(resolve => {
setTimeout(() => resolve(), 1000)
})
}
function slowFunction2() {
return new Promise(resolve => {
setTimeout(() => resolve(), 1000)
})
}
console.log("synch 1");
slowFunction1().then(() => {
slowFunction2().then(() => {
console.log("synch 2");
});
})This code should wait 1 second for each function before it console.log()'s "synch 2"
OR, you could use async/await instead of using .then(), like this:
function slowFunction1() {
return new Promise(resolve => {
setTimeout(() => resolve(), 1000)
})
}
function slowFunction2() {
return new Promise(resolve => {
setTimeout(() => resolve(), 1000)
})
}
async function main() {
console.log("synch 1");
await slowFunction1()
await slowFunction2()
console.log("synch 2");
}
main()
You got this right,you are trying to achieve a asychronous task.
Asynchronous Task
A task which will take some time to complete.
Way 1 - Callbacks
You need to give a callback to your further task. Let me give you an example.
function myHugeTask(callback) {
// I need to do my task
console.log('Hey I am first task')
callback()
}
const someTaskWhichINeedToExecuteLater = () => {
console.log('Hey I am after the first task')
}
myHugeTask(someTaskWhichINeedToExecuteLater)Way 2 - Promises
Promises is like a real world promise. If I promised you then I will either complete it or reject it.
Let see
const myHugeTaskPromise = new Promise(resolve => {
// Do my huge task no matter how much time it takes
console.log('I will complete first')
resolve()
})
myHugeTaskPromise.then(()=>{
console.log('Need to done when my promise get fulfilled')
})