> For the complete documentation index, see [llms.txt](https://docs.evt.land/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.evt.land/api/evt/waitfor.md).

# evt.waitFor(...)

Method that returns a promise that will resolve when the next matched event is posted.

## Without timeout

By default the promise returned by `waitFor` will never reject.

```typescript
import { Evt } from "evt";

const evtText = Evt.create<string>();

setTimeout(()=> evtText.post("Hi!"), 1500);

(async ()=>{

    //waitFor return a promise that will resolve next time 
    //post() is invoked on evtText.
    const text = await evtText.waitFor();

    console.log(text);

})();
```

[**Run the example**](https://stackblitz.com/edit/evt-cazqyr?embed=1\&file=index.ts\&hideExplorer=1)

## With timeout

As with `attach*`, it is possible to set what is the maximum amount of time we are willing to wait for the event before the promise rejects.

```typescript
import { Evt, TimeoutEvtError } from "evt";

const evtText = Evt.create<string>();

(async ()=>{

    try{

        const text = await evtText.waitFor(500);

        console.log(text);

    }catch(error){

        console.assert(error instanceof TimeoutEvtError);
        //Error can be of two type:
        //  -EvtError.Timeout if the timeout delay was reached.
        //  -EvtError.Detached if the handler was detached before 
        //  the promise returned by waitFor have resolved. 

        console.log("TIMEOUT!");

    }

})();

//A random integer between 0 and 1000
const timeout= ~~(Math.random() * 1000);

//There is a fifty-fifty chance "Hi!" is printed else it will be "TIMEOUT!".
setTimeout(
    ()=> evtText.post("Hi!"), 
    timeout
);
```

[**Run the example**](https://stackblitz.com/edit/evt-wqh856?embed=1\&file=index.ts\&hideExplorer=1)

## Subtilities of `evt.waitFor(...)`&#x20;

```typescript
import { Evt } from "evt";

const evtText = Evt.create<string>();

(async ()=>{

    //const firstLetter = await new Promise(resolve=> evtText.attachOnce(resolve));
    const firstLetter = await evtText.waitFor();
    //const secondLetter = await new Promise(resolve=> evtText.attachOnce(resolve));
    const secondLetter = await evtText.waitFor();


    console.log(`${firstLetter} ${secondLetter}`);

})();

evtText.post("A");
evtText.post("B");

//"A B" is printed to the console.  
// Now, if you comment out the implementation using .attachOnce you'll see that
// the second letter is lost, we never reach the console.log
```

[Playground](https://stackblitz.com/edit/evt-playground-34zdzv?file=index.ts)


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.evt.land/api/evt/waitfor.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.