TypeScript - what type is setInterval

Question

If I'd like to assign a type to a variable that will later be assigned a setInterval like so:

this.autoSaveInterval = setInterval(function(){
      if(this.car.id){
        this.save();
      }
      else{
        this.create();
      }
    }.bind(this), 50000);

What type should be assigned to this.autosaveInterval vairable?

Wongawonga

public autoSaveInterval :number; – Smell

You don't need to specify a type; autoSaveInterval will infer its type from the return value of the setInterval call. In browser platforms this is number, but in node.js it's a Timer – Deface

Related github issue: github.com/microsoft/TypeScript/issues/842 – Guerin

Answer 1

Late to the party, but the best type (especially since the type is opaque, we only care that we can pass it to clearInterval() later) might be the automatically deduced one, ie. something like:

ReturnType<typeof setInterval>

Impudicity

Man, this should definitely have been picked as the correct answer. "number" doesn't work, especially in angular – Twylatwyman

I'm joining the party, number didn't work for me either, thank you!! – Complect

Cleanest way of solving the problem, and works in all environments – Shiksa

Wow, didn't know about ReturnType. That's huge! – Griefstricken

ChatGPT couldn't figure this one out, so thank you for this. – Malicious

It should also be noted that according to the @types/node package, v16 setInterval returns NodeJS.Timer, while v18 setInterval returns NodeJS.Timeout. This answer's method is superior for migration concerns because using ReturnType will always be correct. – Trimetric

Answer 2

The type depends on which function you are going to use there are 2 overloads, the return type is marked in red bounding-box :

In order to use the one which returns number, please use :

window.setInterval(...)

Fuddyduddy

Could you share the website or book you got this reference?Thanks. – Heliograph

Hi this is not a book you can find it if you working with visual studio and search for implementation . – Fuddyduddy

In browsers environment, it should be window.setInterval and the return type is number as it is. – Dative

Yes this worked for me and I set the type as let intervalId: number | undefined = undefined; – Hippie

Answer 3

The type is number;

private autoSaveInterval: number = setInterval(() => {
  console.log('123');
}, 5000);

Acne

@gfels Because setInterval return that representing the ID value of the timer that is set. You can use this value with the clearInterval() method to cancel the timer. It's not a function because you are not assigning the function handler to it, you are assigning the result/return value of a function to it. – Acne

If you are using TypeScript, and you get compiler errors because somehow the NodeJS.Timer type is inferred: change to window.setInterval to specify you're not using node and the DOM type should be used, which is number indeed. – Providential

It's not number in node.js – Antisana

Answer 4

I believe its NodeJS.Timeout and widow.setInterval is number:

const nodeInterval: NodeJS.Timeout = setInterval(() => {
  // do something
}, 1000);

const windowInterval: number = window.setInterval(() => {
  // do something
}, 1000);

Scofflaw

The type it's not NodeJS.Timeout but NodeJS.Timer – Sorci

What is the NodeJs type? where it comes from? – Began

Answer 5

As it's mentioned in other answers, the type of setInterval is either :number or :NodeJS.Timer.

I would like to extend the scope of the answer a little bit if anyone is looking to use setInterval with React and Typescript

const Clock: React.FC = () => {
  const secondsRef = useRef<NodeJS.Timer>();

  useEffect(() => {
    secondsRef.current = setInterval(() => { // type is taken correctly and no errors
      // do your stuff...
    }, 1000);
  }, []);

  return (
    <div>
      {/* your jsx... */}
    </div>
  );
};

export default Clock;

Hope someone will find my answer helpful... happy coding :)

Myasthenia

Answer 6

For something like this, it is treated as an opaque handle, it isn't worth struggling with types just to satisfy the windows vs node environments. Just use this and be done with it:

let timerHandle: any = null;

function start() {
  timerHandle = setInterval(...);
}

export function stop() {
  if (timerHandle) clearInterval(timerHandle);
}

Soninlaw

Answer 7

Although i was able to run the app with

id: number;

this.id = setInterval(...)

a test will inform you that Type 'Timeout' is not assignable to type 'number' so i went with https://mcmap.net/q/179865/-typescript-what-type-is-setinterval approach, that worked for me.

Juice

Answer 8

This is the type for setInterval: NodeJS.Timer

Capwell

Answer 9

Use typeof operator to find data type of any variable like this:

typeof is an unary operator that is placed before a single operand which can be of any type. Its value is a string that specifies the type of operand.

var variable1 = "Hello";
var autoSaveInterval;

this.autoSaveInterval = setInterval(function(){
      if(this.car.id){
        this.save();
      }
      else{
        this.create();
      }
    }.bind(this), 50000);
    
console.log("1st: " + typeof(variable1))
console.log("2nd: " + typeof(autoSaveInterval ))

Luzern

This is not helping with Typescript definitions – Oogonium

This does not contain any reference to the original question regarding TypeScript types – Hydrogenous