Uncaught in promise syntaxerror: unexpected end of input

Uncaught in promise syntaxerror: unexpected end of input

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The uncaught in promise syntaxerror: unexpected end of json input is a JavaScript error that usually happens when working with promises.

If you’re stuck and get perplexed by this error message, then keep on reading!

In this article, we will delve into the solutions on how to solve the syntaxerror unexpected end of input, an uncaught in promise syntax error.

What is the promise of Java Script?

In JavaScript, a promise is an object that represents the outcome of an asynchronous operation. It can either be successful or result in failure.

Promises are used to handle asynchronous actions by associating handlers with their eventual success value or failure reason.

They allow asynchronous methods to provide values similar to synchronous methods. Instead of immediately returning the final value, asynchronous methods return a promise, which will eventually provide the value at a later point in time.

If you encounter a reference to a promise in an error message, it indicates that the error happened within the context of a promise.

What is “uncaught in promise syntaxerror unexpected end of json input”?

The error message uncaught in promise syntaxerror: unexpected end of input occurs when the response you get isn’t a JSON.

It can also happen when the JSON you’re getting from the server is invalid or incomplete.

In addition to that, the syntaxerror unexpected end of input error message indicates that there is a problem with the data being received or with how it is being handled in the code.

Why does the uncaught (in promise) “syntaxerror unexpected end of input”?

The uncaught syntaxerror: unexpected end of input error usually happens due to various reasons, such as:

👉 Missing or incomplete code.

👉 Small mistakes like typos, misplaced characters, or missing keywords can cause the code to stop suddenly, disrupting its normal flow.

👉 Forget to include a closing parenthesis, bracket, or quote.
👉 Attempting to parse an empty response using functions like JSON.parse() or $.parseJSON.

👉 Receiving a response from a server in the format of text/html or not receiving any response at all and attempting to parse it as JSON.

How to fix the “uncaught in promise syntaxerror: unexpected end of input”

To fix the uncaught (in promise) syntaxerror: unexpected end of input error, you have to identify the cause of the error first and then address it.

Here are the following solutions that you can use as your bases to easily resolve the error:

Solution 1: Verify promise chaining

Ensure that you correctly chain your promises by returning the subsequent promise within each .then() or .catch() block.

Here’s an example of incorrect code:

function fetchData() {
    return new Promise(resolve => {
        fetch('https://api.sample.com')
            .then(response => response.json())
            .then(data => resolve(data));
    })
    .catch(error => console.log(error));
}

The problem with the provided code above is that the subsequent promise is not returned inside the .then() block, causing an unexpected end of input.

To fix this, simply add the return statement for the subsequent promise.

Corrected code:

function fetchData() {
    return new Promise(resolve => {
        return fetch('https://api.sample.com')
            .then(response => response.json())
            .then(data => resolve(data));
    })
    .catch(error => console.log(error));
}

Solution 2: Ensure Proper Syntax

Verify that your code has proper syntax, including correct placement of commas, semicolons, and parentheses.

Here’s an example of incorrect code:

function fetchData() {
    return new Promise((resolve, reject) => {
        fetch('https://api.sample.com')
            .then(response => response.json())
            .then(data => resolve(data))
            .catch(error => reject(error))
    });
}

In the example code above, there is a missing semicolon after the .catch() block, which leads to a syntax error. To fix this, simply add the semicolon at the end of the line.

Corrected code:

function fetchData() {
    return new Promise((resolve, reject) => {
        fetch('https://api.sample.com')
            .then(response => response.json())
            .then(data => resolve(data))
            .catch(error => reject(error));
    });
}

Solution 3: Check the response before parsing

Before attempting to parse a response as JSON, it is important to check the ok property of the response object to ensure that the request was successful.

If the request was not successful, handle the error in an appropriate manner.

For example:

fetch('<URL>')
  .then(response => {
    if (!response.ok) {
      throw new Error(`An error occurred: ${response.status}`);
    }
    return response.json();
  })
  .then(data => console.log(data))
  .catch(error => console.error(error));

In this example, we are verifying the ok property of the response object to ensure the success of the request.

If the request was not successful, we throw an error message that includes the response’s status code.

On the other hand, if the request was successful, we utilize the json() method to parse the response into JSON format.

Solution 4: Use a fallback value

If you anticipate that a JSON response could potentially be invalid or incomplete, you have the option to provide a fallback value that will be used in case an error occurs.

This fallback value serves as an alternative option to handling situations where the JSON response is not as expected.

For example:

fetch('<URL>')
  .then(response => response.text())
  .then(text => {
    let data;
    try {
      data = JSON.parse(text);
    } catch (error) {
      data = { error: 'Invalid JSON' };
    }
    console.log(data);
  })
  .catch(error => console.error(error));

Solution 5: Check the validity of the JSON response

If you encounter an error while attempting to parse a JSON response from a server, it is essential to ensure that the server is returning valid JSON. To validate the JSON response, you can utilize a tool like JSONLint.

This tool helps in confirming the correctness and validity of the JSON data returned by the server.

For example:

fetch('<URL>')
  .then(response => response.text())
  .then(text => {
    try {
      const data = JSON.parse(text);
      console.log(data);
    } catch (error) {
      console.error('Invalid JSON:', text);
    }
  })
  .catch(error => console.error(error));

In here, we used the text() method to retrieve the response as text. Subsequently, we make use of a try…catch block to try parsing the response text as JSON.

In the event that the parsing fails, we catch the error and log an error message that includes the invalid JSON text.

This approach allows us to handle situations where the response text is not valid JSON and respond accordingly.

Conclusion

In conclusion, the error message uncaught in promise syntaxerror: unexpected end of input occurs when the response you get isn’t a JSON. It can also happen when the JSON you’re getting from the server is invalid or incomplete.

To fix this error you have to identify the cause of the error first and then address it.

This article already provides solutions to fix this error message. By executing the solutions above, you can master this SyntaxError with the help of this guide.

You could also check out other SyntaxError articles that may help you in the future if you encounter them.

We are hoping that this article helps you fix the error. Thank you for reading itsourcecoders 😊

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