Ajax跨域时出现Access to XMLHttpRequest at *** from origin *** has been been blocked by CORS policy

问题截图

发送 ajax 时出现如下错误：

Access to XMLHttpRequest at 'localhost:3000/' from origin 'http://localhost:3000' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome-extension, edge, https, chrome-untrusted.

翻译：

CORS策略已阻止从源'http://localhost:3000'访问'localhost:3000/'处的XMLHttpRequest:跨源请求仅支持协议方案：http、data、chrome、chrome扩展、https。

骚年，我猜你一定把 ajax 写成了这样：

$.ajax({
    
    
    async: true,
    url: 'localhost:3000/',
    type: 'post',
    ...
})

在 url 地址前加上 http:// 就可以了。

$.ajax({
    
    
    async: true,
    url: 'http://localhost:3000/',
    type: 'post',
    ...
})