<?php
    $ar = array('1-21-2018' => 2, '1-23-2018' => 3, '1-18-2018' => 6, '1-26-2018' => 4);
    $json = json_encode($ar);
    echo $json;
    $json_array  = json_decode($json, true);
    $elementCount  = count($json_array);
?>

<script type="text/javascript">
    var data = '<?php echo $json; ?>';
    var json = JSON.parse(data);
    var length = <?php echo $elementCount; ?>;
    console.log(length);
    console.log(json);
    var length = <?php echo $elementCount; ?>;
    for(var i = 0; i < length; i++) {
        console.log(json[i]);
    }
</script>