Fetch API, Chrome, and 404 Errors [duplicate]

问题

I'm playing around with fetch, and I noticed that only Chrome displays an error when a resource I am fetching doesn't exist (aka a 404):

Both Edge and Firefox don't do that, and 404 errors using fetch don't seem to trigger a NetworkError to have my catch error handler to get notified. What should I do to avoid this error in Chrome?

In case you need this, my full code looks as follows:

fetch("https://www.kirupa.com/book/images/learning_react2.gif", {
    method: "head",
    mode: "no-cors"
})
.then(function(response) {
    if (response.status == 200) {
        console.log("file exists!");
    } else {
        console.log("file doesn't exist!");
    }
    return response.text();
})
.catch(function(error) {
  console.log("Error ", error);
});

Thanks, Kirupa

回答1:

only Chrome displays an error when a resource I am fetching doesn't exist (aka a 404)

I'm seeing this as an error in Firefox, Chrome, and Safari.

Code I'm using

I tried to replicate what you're saying using the following run with http-server. There is no "data.json" file.

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <title>Async Test</title>
    <script src="index.js"></script>
</head>

<body>
    <main>
        <h1>Async Test</h1>
    </main>
</body>

</html>

index.js

(async function() {
  let a;
  try {
    a = await fetch("./data.json", {
      method: "head"
    });
    console.log("No error");
  } catch (err) {
    console.log("Caught an error");
  }
  console.log(a);
}());

(function() {
  fetch("./data.json", {
      method: "head"
    })
    .then(data => {
      console.log("No error");
      console.log(data);
    })
    .catch(err => {
      console.log("Caught an error");
    });
}());

Dev Tools Screenshots

Chrome

Firefox

Safari

Analysis

The only way for the browser to know whether the resource exists is to actually make the network request. Chrome always logs network request errors like 404. It's why you probably see a lot of errors about favicons when a site you visit doesn't have one.

You can't force your client to not see them with your own code, but a user can opt in to have the error not show up for them by changing their own browser settings. See this answer to Suppress Chrome 'Failed to load resource' messages in console.

回答2:

You can try to handle the error yourself and actually trigger a Promise.reject(). Something like this

fetch("https://httpstat.us/500", {
    method: "head",
    mode: "no-cors"
})
.then(status)
.then(res => res.json())
.catch(function(error) {
    console.log("Error", error);
});

function status(response) {   
    if (response.ok) {
        return response;
    }
    return response.json().then(res => Promise.reject(res));
}

回答3:

You can try pass function which is called when promise is rejected. You can do that by passing second function in then

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise

回答4:

I would like to share this code snippet to show another way of using promise chain while fetching through an API.

<script>
let url = "https://jsonplaceholder.typicode.com/todos/1";

fetchApi(url);

function handleData(data){
  console.log('succesfull:', data)
}

function fetchApi(url){
  fetch(url)
    .then(response => response.ok ? response.json() : Promise.reject({err: response.status}))
    .then(data => handleData(data))
    .catch(error => console.log('Request Failed:', error));
}

</script>

来源：https://stackoverflow.com/questions/44019776/fetch-api-chrome-and-404-errors

标签

javascript

google-chrome

fetch-api