Set zoom level for Advanced Custom Fields map field.

adminMaps.js

var googleMapsLoaded = false;
var timeout;

if(googleMapsLoaded === false) {
    timeout = setInterval("checkVariable()", 500);
}

function doGoogleMapsHook() {
    // set current zoom level
    var currentZoom = parseInt(jQuery('#acf-field-zoom_level').val());
    acf.fields.google_map.map.setZoom(currentZoom);
    // disable scrollwheel zooming
    acf.fields.google_map.map.setOptions({'scrollwheel': false});
    // update zoom level in field on change
    google.maps.event.addListener( acf.fields.google_map.map, 'zoom_changed', function( e ) {
        var zoom = acf.fields.google_map.map.zoom;
        // update input
        jQuery('#acf-field-zoom_level').val( zoom );
    });
}

function checkVariable() {
    if((typeof google !== 'undefined') && (acf.fields.google_map.map)){
        googleMapsLoaded = true;
        clearInterval(timeout);
        doGoogleMapsHook();
    }
}

functions.php

<?php

function jsAdminMaps($hook) {
    if( 'post.php' != $hook )
        return;
    wp_enqueue_script( 'jsAdminMapsCustom', get_template_directory_uri() . '/js/adminMaps.js', array('jquery'), '0.0.1', true );
}
add_action( 'admin_enqueue_scripts', 'jsAdminMaps' );