Passing PHP JSON to Javascript: echo json_encode vs echo json declaration

<?php
$array = array("const1" => "val", "const2" => "val2");
?>
<script>
var contants = <?php echo json_encode($array); ?>
</script>

$array["<key>"]

contants.const1, ....

// holds variables from PHP
var stuff = {};
try {
    // stuff will always be an object
    stuff = JSON.parse('<?php echo empty($stuff) ? '{}' : json_encode($stuff) ?>');
} catch (e) {
    if (e instanceof SyntaxError)
    {
        // report syntax error
        console.error("Cannot parse JSON", e);
    }
}
// show resulting object in console
console.log("stuff:", stuff);

$array = array("const1" => "val", "const2" => "val2");

echo json_encode($array);

"{\"const1\": \"val\", \"const2\": \"val2\"}"

$json_array = array(
    "const1" => "val",
    "const2" => "val2"
);

$json_obj = json_encode($json_array);

var locations = <?php echo json_encode($sample_location_master); ?>;