How I add Headers to http.get or http.post in Typescript and angular 2?

I have used below code in Angular 9. note that it is using http class instead of normal httpClient.

1. so import Headers from the module, otherwise Headers will be mistaken by typescript headers interface and gives error

   import {Http, Headers, RequestOptionsArgs } from "@angular/http";

2. and in your method use following sample code and it is breaked down for easier understanding.

   let customHeaders = new Headers({ Authorization: "Bearer " + localStorage.getItem("token")});
   const requestOptions: RequestOptionsArgs = { headers: customHeaders };
   return this.http.get("/api/orders", requestOptions);
   

You can define a Headers object with a dictionary of HTTP key/value pairs, and then pass it in as an argument to http.get() and http.post() like this:

const headerDict = {
  'Content-Type': 'application/json',
  'Accept': 'application/json',
  'Access-Control-Allow-Headers': 'Content-Type',
}

const requestOptions = {                                                                                                                                                                                 
  headers: new Headers(headerDict), 
};

return this.http.get(this.heroesUrl, requestOptions)

Or, if it's a POST request:

const data = JSON.stringify(heroData);
return this.http.post(this.heroesUrl, data, requestOptions);

Since Angular 7 and up you have to use HttpHeaders class instead of Headers:

const requestOptions = {                                                                                                                                                                                 
  headers: new HttpHeaders(headerDict), 
};

Be sure to declare HttpHeaders without null values.

    this.http.get('url', {headers: new HttpHeaders({'a': a || '', 'b': b || ''}))

Otherwise, if you try to add a null value to HttpHeaders it will give you an error.