How to post associative array in ionic 3

#1

When i try to post a data in associative array to rest api using ionic.
Only empty data receive in server side.
Is this method is correct or suggest any other method

    public login(credentials) {
   
    let apiUrl = this.urlService.apiUrl  + 'oauth/access_token';
    let headers = new Headers({'Content-Type' : 'application/x-www-form-urlencoded'});
    let options = new RequestOptions({
			headers: headers});
    
     var postcredn=new Array();

     postcredn['username'] = "karthik@w3cert.in";
     postcredn['password'] = "05550";
     postcredn['grant_type'] = "password";
     postcredn['client_id'] = "Outfit1548925669";
     postcredn['client_secret'] = "a10620c85033ab02b582d17716cda245";

 
    console.log('iii'+postcredn['username'] );
    
      return new Promise((resolve, reject) => {
          this.http.post(apiUrl, postcredn,  options)
         
           .subscribe(res => {
            resolve(JSON.parse(JSON.stringify(res)));
             console.log('json'+ JSON.stringify(postcredn));
        
           }, (err) => {
             reject(err);
   public login(credentials) {
   
    let apiUrl = this.urlService.apiUrl  + 'oauth/access_token';
    let headers = new Headers({'Content-Type' : 'application/x-www-form-urlencoded'});
    let options = new RequestOptions({
			headers: headers});
    
     var postcredn=new Array();

     postcredn['username'] = "karthik@abcde.in";
     postcredn['password'] = "05550";
     postcredn['grant_type'] = "password";
     postcredn['client_id'] = "Outfit1548669";
     postcredn['client_secret'] = "a10620c85033abd17716cda245";

 
    console.log('iii'+postcredn['username'] );
    
      return new Promise((resolve, reject) => {
          this.http.post(apiUrl, postcredn,  options)
         
           .subscribe(res => {
            resolve(JSON.parse(JSON.stringify(res)));
             console.log('json'+ JSON.stringify(postcredn));
        
           }, (err) => {
             reject(err);
             console.log(apiUrl);
           });
     });
    }
        
}           console.log(apiUrl);
           });
     });
    }
        
}

Thanks in advance