Access Control Allow Origin issue in Angular 2

Question

I have a problem with getting data from my node.js server.

The client side is:

    public getTestLines() : Observable<TestLine[]> {
    let headers = new Headers({ 'Access-Control-Allow-Origin': '*' });
    let options = new RequestOptions({ headers: headers });

    return this.http.get('http://localhost:3003/get_testlines', options)
                .map((res:Response) => res.json())
                .catch((error:any) => Observable.throw(error.json().error || 'Server error')); 
}

in server side I also set the headers:

resp.setHeader('Access-Control-Allow-Origin','*') 
resp.send(JSON.stringify(results))

But I get an error

"XMLHttpRequest cannot load http://localhost:3003/get_testlines. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access."

How can I fix it? When I remove headers it says that this header is required.

Answer 1

Access-Control-Allow-Origin is a response header, not a request header.

You need to have it appear on the response, not the request.

You have attempted to put it on the response:

resp.setHeader('Access-Control-Allow-Origin','*') 

… but it hasn't worked.

This is probably because you haven't put it on the response to the right request. The error message says:

Response to preflight request doesn't pass access control check

You have done something to make the request preflighted. This means that before the browser makes the GET request you are trying to make, it is making an OPTIONS request.

This is, presumably, being handled by a different piece of code on your server so the line resp.setHeader('Access-Control-Allow-Origin','*') isn't being hit.

One thing that causes a preflighted request to be made is the addition of request headers (other than a small number of exceptions). Adding Access-Control-Allow-Origin to the request will trigger a preflighted request, so the first thing to do to try to fix the problem is to remove Access-Control-Allow-Origin from the request.

If that fails, then you need to set up your server so it can respond to the OPTIONS request as well as the GET request.

Answer 2

Access-Control-Allow-Origin is a response header, not a request header you need to fix the permission in your backend. so you must create cors.js file that contains all necessary permissions.

function crosPermission(){
  this.permission=function(req,res,next){
    res.header('Access-Control-Allow-Origin','*');
    res.header('Access-Control-Allow-Headers','Content-Type');
    res.header('Access-Control-Allow-Methods','GET','POST','PUT','DELETE','OPTIONS');
    next();
  }
}

module.exports= new crosPermission();

next step You need to add some line in your app.js

    var cors=require('./cors');
    app.use(cors.permission)