Ajax-18: Same-origin policy

What is the Same Origin Policy?

The same-origin policy is a security policy of the browser. Same origin means that the protocol, domain name, and port number must be exactly the same. Violating the same origin policy is cross-domain .

Access URL under the same origin can be abbreviated

const btn = document.querySelector('button');

btn.onclick = function() {
    
    
    const xhr = new XMLHttpRequest();
    // 因为满足同源策略，所以url路径可以简写
    xhr.open('GET','/data');
    xhr.send();
    xhr.onreadystatechange = function() {
    
    
        if(xhr.readyState === 4) {
    
    
            if(xhr.status >= 200 && xhr.status < 300) {
    
    
                console.log(xhr.response);
            }
        }
    }            
}

Precautions

• The webpage opened by the right-click of VScode is port 5500. When testing, we must see if the port set is consistent with our server port. Once inconsistent, cross-domain problems will occur.