How to Use the json_last_error_msg Function to Optimize Data Transmission Between Frontend and Backend?

In modern web development, data exchange between the frontend and backend heavily relies on the JSON format. The frontend packages data into a JSON object using JavaScript and sends it to the backend, which then parses and processes the JSON string using PHP. However, during transmission and parsing, errors such as encoding issues, missing quotes, or syntax inconsistencies can easily occur. If these errors are not captured promptly, they could lead to program malfunctions or even data loss. To better optimize the data transmission format between frontend and backend, the `json_last_error_msg()` function becomes a highly useful tool.

1. What is `json_last_error_msg()`?

In PHP, when using `json_encode()` or `json_decode()` functions, errors may arise. PHP provides `json_last_error()` to return error codes, but these codes are numerical and not very intuitive. On the other hand, `json_last_error_msg()` returns a corresponding error message string, which is much easier for developers to understand and debug.

Example:

<?php
$data = '{"invalidJson": true}'; // Invalid JSON string
$result = json_decode($data, true);

if (json_last_error() !== JSON_ERROR_NONE) {
    echo "Parsing failed: " . json_last_error_msg();
}
?>

The output might be:

Parsing failed: Syntax error

With this, developers can quickly pinpoint the issue instead of solely relying on error codes.

2. The Importance of Optimizing Data Transmission Between Frontend and Backend

1. Ensuring Data Integrity: If the data structure is corrupted during transmission, errors can be detected and the frontend can be notified for correction.
2. Improving User Experience: Clear and straightforward error messages help the frontend quickly locate the problem, reducing communication costs.
3. Enhancing System Robustness: An error detection mechanism can prevent business logic interruption caused by parsing errors.

3. Practical Use Cases

1. Validating Data When Receiving from the Frontend

<?php
// Assume the frontend sends JSON data via AJAX
$jsonInput = file_get_contents("php://input");
$data = json_decode($jsonInput, true);

if (json_last_error() !== JSON_ERROR_NONE) {
    http_response_code(400);
    echo json_encode([
        "status" => "error",
        "message" => "Invalid JSON format: " . json_last_error_msg()
    ]);
    exit;
}

// If the data format is correct, continue with the business logic
echo json_encode([
    "status" => "success",
    "data" => $data
]);
?>

In this way, the backend can detect JSON parsing issues immediately and return a user-friendly error message.

2. Checking Data When Sending to the Frontend

<?php
$response = [
    "status" => "success",
    "message" => "Operation completed",
    "data" => [
        "id" => 123,
        "name" => "Test User"
    ]
];

$jsonOutput = json_encode($response);

if (json_last_error() !== JSON_ERROR_NONE) {
    error_log("JSON encoding failed: " . json_last_error_msg());
    http_response_code(500);
    echo "Server data format error";
    exit;
}

echo $jsonOutput;
?>

This ensures that the JSON data returned from the backend to the frontend is always valid and parsable.

4. Conclusion

JSON is the core format for data transmission between the frontend and backend. However, errors can inevitably occur during processing. `json_last_error_msg()` provides developers with an intuitive way to capture and describe errors, helping to quickly locate problems and significantly improving system robustness and user experience. By properly applying this function during data reception and output stages, the data transmission format between frontend and backend can be effectively optimized, making the system more stable and reliable.