<?php
    $ar = array('01\21\2018' => '2', '01\22\2018' => '3', '01\18\2018' => '6', '01\26\2018' => '4');
    $json = json_encode($ar);
    echo $json;
    $json_array  = json_decode($json, true);
    $elementCount  = count($json_array);
?>

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