如何使用 nodejs 在 mysql 数据库中插入 npm uniqid 模块。 当我输入代码时，它显示错误“TypeError: uniqid is not a function”

Question

I am using nodejs with express and mysql. when i submit a form i found an error "uniqid is not a function".

var express = require('express');
var router = express.Router();
var uniqid = require('uniqid');
var db = require('../db');

router.post('/create',function(req,res,next){
    var full_name = req.body.fullname;
    var email = req.body.email;
    var password= req.body.password;
    var mobile_no = req.body.mobile_no;    
    var uniqid = uniqid();

    var insert_query = `INSERT INTO users (user_uid,full_name,email,mobile_no,password) VALUES ("${uniqid}","${full_name}","${email}","${mobile_no}","${password}") `;

    db.query(insert_query,function(err,result){
      if(err) throw err;
      res.redirect('/signup');
   });
});
module.exports = router;

Answer 1

You're overriding the uniqid module with the value from uniqid()

var uniqid = require('uniqid');
...
var uniqid = uniqid();

While it might work on the first execution ¹ , subsequent calls will fail with that error "uniqid is not a function"

Change the name and use es6 let/const instead of var

const uniqid = require('uniqid');
...
const newId = uniqid();
const insert_query = `INSERT INTO ... VALUES ("${newId}"...) `;

¹ _{It doesn't, see Klaycon comment below}

Answer 2

Let's take this code for example :

 var foo = () => "test" function test() { var foo = foo() } test()

As you can see, it has the same error you have. This is because you are naming your local variable like your global variable.

What happens is what is called Hoisting . When the function gets executed, it declares foo as a variable local to the current function execution context before setting it any value.

Then the engine tries to set its value with foo() , but at that time foo is a local variable, not the global one, and its value is undefined .

And obviously, undefined is not a function, hence the error, "foo is not a function".

tl;dr: be careful when naming your variables (and use let / const ).