js控制台显示[object Object]问题（js向控制台输出信息）

问题描述：在console.log中打印一个json对象时会显示[object Object]

//清空控制台输出并将光标显示在第一排
console.clear();
//定义一个json格式的对象
var j = {};
j.name = "小J";
j.sex = true;
j.age = 19;
//控制台输出
console.log("JSON对象:"+j);
console.log("JSON对象:"+JSON.stringify(j));
console.log(j);
console.log("JSON对象:%o",j);

控制台显示

需要先了解Console对象

Console 对象用于 JavaScript 调试。JavaScript 原生中默认是没有 Console 对象,这是宿主对象（也就是游览器）提供的内置对象。 用于访问调试控制台, 在不同的浏览器里效果可能不同。

console.log()方法可以简单地传递一系列对象，这些对象的字符串表示形式被串联成一个字符串，然后输出到控制台。（以Object.prototype.toString()的方法表示为字符串）

正式因为console.log()在输出多个对象的时候会以字符串的形式串联成一个字符串输出，所以会显示为“JSON对象: [object Object]"。

要想正确显示一个json对象可以单独打印，或者利用JSON.stringify()方法现将要打印的json对象格式化为字符串。

当然console.log()支持字符串替换，所以也可以用字符串替换的方式

%o、%O:输出一个JavaScript对象，在控制台中可以打开有关对象的更多信息。%后面是对象Object的首写字母O

angular – 无法解析AuthenticationService的所有参数：([object Object],？,[object Object])

@Inject(forwardRef(() => AuthenticationService)) public authService: AuthenticationService

import { Injectable } from '@angular/core';
import {Http,Headers,Response} from '@angular/http';
import 'rxjs/add/operator/toPromise';
import {Observable} from 'rxjs/Rx';

import {AppServices} from "../../app.services";
import {Router} from "@angular/router";

@Injectable()
export class AuthenticationService {
  public token: any;

  constructor(
    private http: Http,private appService: AppServices,private router: Router
  ) {
    this.token = localStorage.getItem('token');
  }

  login(username: string,password: string): Observable<boolean> {
    let headers = new Headers();
    let body = null;
    headers.append("Authorization",("Basic " + btoa(username + ':' + password)));

    return this.http.post(this.appService.api + '/login',body,{headers: headers})
      .map((response: Response) => {
        let token = response.json() && response.json().token;
        if (token) {
          this.token = token;
          localStorage.setItem('Conform_token',token);
          return true;
        } else {
          return false;
        }
      });
  }

  logout(): void {
    this.token = null;
    localStorage.removeItem('Conform_token');
    this.router.navigate(['/login']);
  }
}

import {Injectable} from '@angular/core';
import {Headers,Http,RequestOptions} from '@angular/http';
import {Router} from "@angular/router";
import {AuthenticationService} from "./auth/auth.service";

import 'rxjs/add/operator/toPromise';
import {Observable} from 'rxjs/Rx';

@Injectable()

export class AppServices {

  api = '//endpoint/';

  public options: any;
  constructor(
    private http: Http,private router: Router,public authService: AuthenticationService // doesn't work
  //  @Inject(forwardRef(() => AuthenticationService)) public authService: AuthenticationService // doesn't work either
      ) {
        let head = new Headers({
      'Authorization': 'Bearer ' + this.authService.token,"Content-Type": "application/json; charset=utf8"
    });
    this.options = new RequestOptions({headers: head});
  }

  // ====================
  //    data services
  // ====================

  getData(): Promise<any> {
    return this.http
      .get(this.api + "/data",this.options)
      .toPromise()
      .then(response => response.json() as Array<Object>)
      .catch((err)=>{this.handleError(err);})
  }

import { browserModule } from '@angular/platform-browser';
import { browserAnimationsModule } from '@angular/platform-browser/animations';

import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import {BaseRequestOptions,HttpModule} from '@angular/http';

import { MaterialModule} from '@angular/material';
import {FlexLayoutModule} from "@angular/flex-layout";
import 'hammerjs';

import { routing,appRoutingProviders }  from './app.routing';
import { AppServices } from './app.services';
import {AuthGuard} from "./auth/auth.guard";
import {AuthenticationService} from "./auth/auth.service";

import {AppComponent} from './app.component';
import {AuthComponent} from './auth/auth.component';
import {NotFoundComponent} from './404/not-found.component';
import { HomeComponent } from './home/home.component';

@NgModule({
  declarations: [
    AppComponent,AuthComponent,NotFoundComponent,HomeComponent
  ],imports: [
    browserModule,browserAnimationsModule,FormsModule,HttpModule,routing,MaterialModule,FlexLayoutModule
  ],providers: [AppServices,AuthGuard,AuthenticationService],bootstrap: [AppComponent]
})
export class AppModule { }

export class AuthenticationService {
  public token: any;
  appService: AppServices;
  constructor(
    private http: Http,// private appService: AppServices,injector:Injector;
    private router: Router
  ) {
    setTimeout(() => this.appService = injector.get(AppServices));
    this.token = localStorage.getItem('token');
  }

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