JavaScript fetch - Failed to execute 'json' on 'Response': body stream is locked

I met this error too but found out it is not related to the state of Response, the real problem is that you only can consume Response.json() once, if you are consuming it more than once, the error will happen.

like below:

    fetch('http://localhost:3000/movies').then(response =>{    console.log(response);    if(response.ok){         console.log(response.json()); //first consume it in console.log        return response.json(); //then consume it again, the error happens    }

So the solution is to avoid consuming Response.json() more than once in then block.

According to MDN, you should use Response.clone():

The clone() method of the Response interface creates a clone of a response object, identical in every way, but stored in a different variable. The main reason clone() exists is to allow multiple uses of Body objects (when they are one-use only.)

Example:

fetch('yourfile.json').then(res=>res.clone().json())

Response methode like 'json', 'text' can be called once, and then it locks.The posted image of response shows that body is locked.This means you have already called the 'then', 'catch'. To reslove this you can try the following.

fetch(url)    .then(response=> response.body.json())    .then(myJson=> console.log(myJson))

Or

fetch(url)    .catch(response=> response.body.json())    .catch(myJson=> console.log(myJson))