javascript-使用http拦截器设置来自离子存储的默认请求标头-Angular 5-Ionic 3

我正在尝试使用angular 5新的HTTP客户端在所有请求标头中设置令牌值.下面是我的代码：

import {Injectable} from '@angular/core';
import {HttpEvent, HttpInterceptor, HttpHandler, HttpRequest} from '@angular/common/http';
import {Observable} from "rxjs/Observable";
import { Storage } from '@ionic/storage';
import {Globals} from '../globals/globals';

@Injectable()
export class Interceptor implements HttpInterceptor {
  token: string;
  constructor(private storage: Storage, private global: Globals){ 
    this.storage.get('token').then((val) => {
      this.token = val;
    });
  }

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    console.log(this.token) //undefined "only for first time on app start"
    req = req.clone({
      setHeaders: {
        'Token': this.token,
        'Version': this.global.version,
      }
    });
    return next.handle(req);
  }
}

虽然在请求标头中添加令牌很有效,但是有一个严重的异常.第一次不起作用.问题在于js异步性质,req.clone在从存储中获取令牌之前就已执行.由于离子存储还应许,那么如何首次处理这种情况？

解决方法:

您可以合并两个异步请求(获取令牌和处理请求),以在令牌准备就绪时执行稍后的操作(而不是在构造函数中获取)：

// -------------------------------------------------------------------------
// Please note that I'm using lettable/pipeable operators (RxJS > 5.5.x)
// https://github.com/ReactiveX/rxjs/blob/master/doc/pipeable-operators.md
// -------------------------------------------------------------------------

import { Injectable } from '@angular/core';
import { HttpEvent, HttpInterceptor, HttpHandler, HttpRequest } from '@angular/common/http';
import { Observable } from "rxjs/Observable";
import { Storage } from '@ionic/storage';
import { Globals } from '../globals/globals';

// New imports!
import { fromPromise } from 'rxjs/observable/fromPromise';
import { mergeMap } from 'rxjs/operators/mergeMap';

@Injectable()
export class Interceptor implements HttpInterceptor {

  constructor(private storage: Storage, private global: Globals){ }

  getToken(): Promise<any> {
    return this.storage.get('token');
  }

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return fromPromise(this.getToken()).pipe(
        mergeMap(token => {

            // Use the token in the request
            req = req.clone({
                setHeaders: {
                    'Token': token,
                    'Version': this.global.version,
                }
            });

            // Handle the request
            return next.handle(req);
        }));
  }
}

标签：angular,typescript,ionic2,ionic3,javascript
来源： https://codeday.me/bug/20191025/1928509.html