Proof of Work 示例：验证你的输入

<html>
<head>
<title>Proof of Work 示例</title>
</head>
<body>
<h1>Proof of Work 示例</h1>
<p>原理非常简单，就是我这有20位随机数，提供给你它们的哈希值，和后面16位的值，你写前四位就好了。至于为什么要有这个，假如我做的是网站，防DDOS攻击就很有必要了。</p>
<p id="proof"></p>
<form onsubmit="return submitForm()">
<label for="input">请输入前四位：</label>
<input type="text" id="input" name="input" maxlength="4">
<input type="submit" value="提交">
</form>
<p id="result"></p>
<script>
function generateProof() {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById("proof").innerHTML = this.responseText;
}
};
xhr.open("GET", "/generate_proof", true);
xhr.send();
}
function submitForm() {
var input = document.getElementById("input").value;
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById("result").innerHTML = this.responseText;
generateProof();
}
};
xhr.open("POST", "/submit_form", true);
xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhr.send("input=" + input);
return false;
}
generateProof();
</script>
</body>
</html>