const express = require("express");
const bodyParser = require("body-parser");
const app = express();
app.get(bodyParser.urlencoded({extended: true}));
app.get("/", function(req, res){
  res.sendFile(__dirname + "/index.html");
});
app.post("/", function(req, res){
console.log(req.body.crypto);
});
app.listen(3000, function(){
  console.log("server is running in port 3000");
});

回答如下：

您的req.body未定义，

您必须填写此行

app.get(bodyParser.urlencoded({extended: true}));

到

app.use(bodyParser.urlencoded({extended: true}));