XMLHttpRequest with Observable in Typescript

问题:

I have a tslint problem when I try to manage the result of an XMLHttpRequest call I do to upload files. Here is my current method I found on the internet :

// Files upload request
makeFileRequest(url: string, files: Array<File>) {
    return new Promise((resolve, reject) => {
        let formData: any = new FormData()
        let xhr = new XMLHttpRequest()
        for(let file of files) {
            formData.append("uploads[]", file, file.name)
        }
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4) {
                if (xhr.status === 200) {
                    resolve(JSON.parse(xhr.response))
                } else {
                    reject(xhr.response)
                }
            }
        }
        xhr.open("POST", url, true)
        xhr.send(formData)
    })
}

So it works, the files are being uploaded and the backend replies a 200 response. But in the method where I use this function, I do this :

        this.makeFileRequest("theurl", this.listFiles)
        .map(res => res.json())
            .subscribe(
                res => console.log(res),
                error => console.log("fails")
            )

But tslint tells me this for at the map point :

TS2339 Property 'map' does not exist on type 'Promise<{}>'.

So I think it would be better to manage the makeFileRequest function so it returns an Observable instead of a Promise. And just in case, note I import "rxjs/add/operator/map".

Has anyone any idea ? Thanks !

回答1:

map is a method of Observable, not Promise. Returning an Observable will fix the error:

makeFileRequest(url: string, files: Array<File>) {
    return Observable.fromPromise(new Promise((resolve, reject) => {
        let formData: any = new FormData()
        let xhr = new XMLHttpRequest()
        for (let file of files) {
            formData.append("uploads[]", file, file.name)
        }
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4) {
                if (xhr.status === 200) {
                    resolve(JSON.parse(xhr.response))
                } else {
                    reject(xhr.response)
                }
            }
        }
        xhr.open("POST", url, true)
        xhr.send(formData)
    }));
}

The solution for the error:

Property 'json' does not exist on type '{}'

https://stackoverflow.com/a/33919897

Don't forget to import Response:

import {Response} from '@angular/http';

回答2:

The simple way to achieve:

xhrCall(url, formData, header) {
    return Observable.create(function (observer) {
      let xhr = new XMLHttpRequest();
      xhr.onreadystatechange = function () {
        if (xhr.readyState == 4) {
          if (xhr.status == 200) {
            observer.next(xhr);
          } else {
            observer.error(xhr);
          }
        }
      };

      xhr.open("POST", url, true);
      xhr.setRequestHeader(header.name, header.value);
      xhr.send(formData);
    });
}