$(document).ready(function () {
// AJAX
$( '#um_form' ).submit( function() {
    // Grab our post meta value
    var um_val = $( '#um_form #um_key' ).val();
    $.post(my_ajax_obj.ajax_url, {         //POST request
       _ajax_nonce: my_ajax_obj.nonce,     //nonce
        action: "my_tag_count",            //action
        'custom_meta': um_val,       // Replace `um_key` with your user_meta key name
    }//,  function() {                    //callback
        //$('#um_key').val(um_val);    //will php be required to place the user id specific value?
    //}
    );
    console.log('um_val: ',um_val);
    // Stop our form from submitting
    return false;
} );
//required post-load event
$( document.body ).trigger( 'post-load' );

//AJAX
$ajax_url = admin_url( 'admin-ajax.php' );        // Localized AJAX URL
// Register Our Script for Localization
wp_register_script(
    'custom',                             // Our Custom Handle
    "/wp-content/themes/myTheme/js/custom.js",  // Script URL, this script is located for me in `theme-name/scripts/um-modifications.js`
    array( 'jquery' ),                              // Dependant Array
    '1.0',                                          // Script Version ( Arbitrary )
    true                                            // Enqueue in Footer
);
// Localize Our Script so we can use `ajax_url`
wp_localize_script( 'custom', 'my_ajax_obj', $ajax_url );
wp_enqueue_script( 'custom' );
}

function my_action() {
// Ensure we have the data we need to continue
if( ! isset( $_POST ) || empty( $_POST ) || ! is_user_logged_in() ) {
    // If we don't - return custom error message and exit
    header( 'HTTP/1.1 400 Empty POST Values' );
    echo 'Could Not Verify POST Values.';
    exit;
}

$user_id = get_current_user_id();
//create custom fields
$initialize = "";
add_user_meta( $user_id, 'custom_meta', $initialize);
//collect & sanitize
$um_val = sanitize_text_field( $_POST['custom_meta'] );
//update info
update_user_meta( $user_id, 'custom_meta', $um_val );

exit;
}

//add AJAX for logged in users only
add_action( 'wp_ajax_my_action', 'my_action' );

$user_id = get_current_user_id();
            //collect data for rendering
            $test1 = get_user_meta( $user_id, 'custom_meta' );
            ?>
            <form id="um_form" method="POST">

        <label for="um_key">
            User Meta Value:
            <input type="text" name="um_key" id="um_key" value="<?php echo
$test1;?>" style="width:100%;" />
        </label>
                <input type="submit" value="Submit" />
        </form>