PHP: How to use PHP variables in js, what to do when php variables are arrays

Method 1: Use embedded PHP script tags

1. Simple splicing

Use the inline PHP script tag <?php ?> to embed the value of the PHP variable $phpVariable into the JavaScript code.

<?php
$phpVariable = "Hello, World!";
?>

<script>
// 将 PHP 变量的值传递给 JavaScript 变量
var jsVariable = '<?php echo $phpVariable; ?>';

// 在 JavaScript 中使用 jsVariable
console.log(jsVariable); // 输出：Hello, World!
</script>

Supplement: Processing when PHP variables are arrays

 

<?php
$phpVariable = ['这是数组第一项', '这是数组第二项'];
?>

<script>
	// 将 PHP 变量的值传递给 JavaScript 变量
	var jsVariable = '<?php echo $phpVariable[0]; ?>';
	// 在 JavaScript 中使用 jsVariable
	alert(jsVariable); // 输出：这是数组第一项
</script>

The above method can output individual items, but if replaced, it cannot be output correctly, as follows

<?php
$phpVariable = ['这是数组第一项', '这是数组第二项'];
?>

<script>
	// 将 PHP 变量的值传递给 JavaScript 变量
	var jsVariable = '<?php echo $phpVariable; ?>';
	// 在 JavaScript 中使用 jsVariable
	alert(jsVariable[0]); // 输出：A
</script>

The output result is the first value of Array.

Solution

通过json_encode() converts a PHP array or object into a JSON string representation

Convert a JSON-formatted string into a JavaScript object or array through JSON.parse().

<?php
$phpVariable = ['这是数组第一项', '这是数组第二项'];
?>

<script>
	// 将 PHP 变量的值传递给 JavaScript 变量
	var jsVariable = JSON.parse('<?php echo json_encode($phpVariable); ?>');
	// 在 JavaScript 中使用 jsVariable
	alert(jsVariable[0]); // 输出：这是数组第一项
</script>

 2. Given a hidden text box to store the value

Store variables through text boxes in a <?php?>

<?php
if (isset($_SESSION['UserID'])) {
	$sql = "
			select  depart_code
			from www_users
			where userid = '" . $_SESSION['UserID'] . "'
		";
	$result = DB_query($sql, $db);
	if ($row = DB_fetch_array($result)) {
		$departCode = $row['depart_code'];
		echo "<input type='hidden' id='departCode' value='" . $departCode . "'>";
		// echo "<script>alert('" . $departCode . "')</script>";
	} else {
		prnMsg(_('找不到相应数据！'), 'error');
	}
}
?>

Get php variables in js

var departCode = document.getElementById('departCode').value;
alert(departCode);

Method 2: Use AJAX request

If you need to dynamically get the value of a PHP variable from the backend, you can use AJAX requests.

1. Page A

Use jQuery's $.ajax() method to make a GET request to the backend PHP file and set JavaScript variables jsVariable based on the returned data.

<!-- 引入 jQuery 库 -->
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>

<script>
$(document).ready(function() {
    $.ajax({
        url: 'get_php_variable.php', // 后端 PHP 文件的路径
        method: 'GET',
        success: function(response) {
            var jsVariable = response; // 根据后端返回的数据设置 JavaScript 变量
            console.log(jsVariable); // 输出从 PHP 获取的变量值
        },
        error: function() {
            console.log('请求失败');
        }
    });
});
</script>

2. Page B

In the backend PHP file get_php_variable.php you can get the value of the PHP variable and return it to the AJAX request if needed. For example:

<?php
$phpVariable = "Hello, World!";
$response = array('phpVariable' => $phpVariable); // 构造响应数据数组
echo $phpVariable;
?>