Access-Control-Allow-Origin - Ajax 请求跨越 CORS解决方案

$(document).ready(function() {
         $("#download").click(function() {
         $.ajax({
           url:'https://api.thingspeak.com/channels/899906/feeds.csv?start=2019-11-08%2019:10:08&end=2019-11-11%2019:11:11',
           crossDomain:true,
           type:'GET',
           data:{
             format:'csv',
           },
           success:function(response){
             window.location.href ='https://api.thingspeak.com/channels/899906/feeds.csv?start=2019-11-08%2019:10:08&end=2019-11-11%2019:11:11' ;
           },
           error:function() {
             $().text("There was an error processing your request.Please try again");
             }
         });
         });

       });

方案二：JSONP

 $.ajax({
        type: "GET",
        headers : {
          "Access-Control-Allow-Origin": "*",
          'Content-Type':'application/json'
        },
        crossDomain:true,
        url: 'https://localhost:44369/api/signList',
        dataType: 'jsonp',
        jsonpCallback: (data)=>{
          console.log(data)
        },
        jsonp: (data)=>{
          console.log(data)
        },
      })

// ajax with cross domain is true
 $.ajax({
        type: "GET",
        crossDomain: true,
        url: 'https://localhost:44369/api/signList',
        dataType: "json",
        success: data => {
            console.log(data)
        },
        error: (err) => {
          console.log('request json error' + err)
        }
      })

方案三，服务端设置 

header("Access-Control-Allow-Origin: *"); # 跨域处理

问题就解决了

1. .net Core (web api)为例子：

在startup.cs 文件中加入如下代码：

 services.AddCors(c =>
            {
                c.AddPolicy("AllowOrigin", options => options.AllowAnyOrigin());
            });
 

app.UseCors(options => options.AllowAnyOrigin());

  public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
            services.AddCors(c =>
            {
                c.AddPolicy("AllowOrigin", options => options.AllowAnyOrigin());
            });

        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            app.UseCors(options => options.AllowAnyOrigin());
        }

运行结果如下：

参考文章：https://www.c-sharpcorner.com/article/enabling-cors-in-asp-net-core-api-application/