I jump into react with just the basic about javascript, I'm making a query in my server that handle mysql and the connection is fine but the return is where I have a problem,it suppose to return a JSON with the query but I found error typeError _ref is undefined here is the function where I connect to my API

callDB(){
    fetch('http://localhost:4000/lista')
    .then((response)=>{
        response.json()
    })
    .then(({data})=>{
        console.log(data);
    })
    .catch((err)=>{console.log(err);});
}

In the data part is where it doesn't work any ideas?thanks before anything

I jump into react with just the basic about javascript, I'm making a query in my server that handle mysql and the connection is fine but the return is where I have a problem,it suppose to return a JSON with the query but I found error typeError _ref is undefined here is the function where I connect to my API

callDB(){
    fetch('http://localhost:4000/lista')
    .then((response)=>{
        response.json()
    })
    .then(({data})=>{
        console.log(data);
    })
    .catch((err)=>{console.log(err);});
}

In the data part is where it doesn't work any ideas?thanks before anything

• javascript
• mysql
• node.js
• reactjs

2 Answers 2

It happens when trying to destructure an object from the undefined value, in your case it's { data }.

So in this particular case returning response.json() from the previous then() handler helps, but other readers may have this problem in other cases as well, in this case you either need to provide a default value like {} or explicitly check for undefined before trying to desctucture

You need to return response.json() in your Promise handler :

callDB(){
    fetch('http://localhost:4000/lista')
    .then((response)=>{
        return response.json()
    })
    .then(({data})=>{
        console.log(data);
    })
    .catch((err)=>{console.log(err);});
}