www.webdeveloper.com
Results 1 to 3 of 3

Thread: defining default values for non-existent properties of an object...

  1. #1
    Join Date
    Dec 2002
    Location
    Seattle, WA
    Posts
    1,843

    defining default values for non-existent properties of an object...

    I have an application that uses callback functions that alter properties of an object, example
    Code:
    function app()
    {
        this.attributes = {
    		"a": 100,
    		"b": 100,
    		"c": 100,
    		"d": 100,
    		"e": 100,
    		"f": 100
    	};
    }
    my callback functions look like this
    Code:
    function()
    {
    	this.attributes["x"] = (this.attributes["x"] || 0) + 100;
    }
    I would like to write it as
    Code:
    function()
    {
    	this.attributes["x"] += 100;
    }
    I know you can use Object.prototype.__proto__ to redefine default values for properties (from null to 0). but does this apply to non-existent properties as well?

  2. #2
    Join Date
    Mar 2009
    Posts
    590
    I am not sure of the context, but you might try something like:

    Code:
    function splint(objThatMakeBeLacking, property){
        var default = 100;
        if(!objThatMakeBeLacking[property]){
             return default;
        }
        else{
              return objThatMakeBeLacking[property];
              }
    
    }

  3. #3
    Join Date
    Dec 2002
    Location
    Seattle, WA
    Posts
    1,843
    After a bit of trying out __proto__, get/set, and a bit googling. I found this post on stackoverflow.
    In short, JavaScript does not permit defining default values for unknown properties.
    Not a big deal, this was just an idea I had to reduce redundancy.
    I'll probably do something like this
    Code:
    function Attributes()
    {};
    Attributes.prototype.add = function(key, value)
    {
        this[key] = (this[key] || 0) + value;
    };
    
    function app()
    {
        this.attributes = new Attributes();
    }
    var app = new app();
    app.attributes.add('x', 100);
    Thanks for the reply nonetheless.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
HTML5 Development Center

"

"

X vBulletin 4.2.2 Debug Information

  • Page Generation 0.08972 seconds
  • Memory Usage 2,858KB
  • Queries Executed 15 (?)
More Information
Template Usage (33):
  • (1)SHOWTHREAD
  • (1)ad_footer_end
  • (1)ad_footer_start
  • (1)ad_global_above_footer
  • (1)ad_global_below_navbar
  • (1)ad_global_header1
  • (1)ad_global_header2
  • (1)ad_navbar_below
  • (1)ad_showthread_firstpost_sig
  • (1)ad_showthread_firstpost_start
  • (1)ad_thread_first_post_content
  • (1)ad_thread_last_post_content
  • (5)bbcode_code
  • (1)footer
  • (1)forumjump
  • (1)forumrules
  • (1)gobutton
  • (1)header
  • (1)headinclude
  • (1)headinclude_bottom
  • (3)memberaction_dropdown
  • (1)navbar
  • (4)navbar_link
  • (1)navbar_moderation
  • (1)navbar_noticebit
  • (1)navbar_tabs
  • (2)option
  • (3)postbit
  • (3)postbit_onlinestatus
  • (3)postbit_wrapper
  • (1)spacer_close
  • (1)spacer_open
  • (1)tagbit_wrapper 

Phrase Groups Available (6):
  • global
  • inlinemod
  • postbit
  • posting
  • reputationlevel
  • showthread
Included Files (26):
  • ./showthread.php
  • ./global.php
  • ./includes/class_bootstrap.php
  • ./includes/init.php
  • ./includes/class_core.php
  • ./includes/config.php
  • ./includes/functions.php
  • ./includes/functions_navigation.php
  • ./includes/class_friendly_url.php
  • ./includes/class_hook.php
  • ./includes/class_bootstrap_framework.php
  • ./vb/vb.php
  • ./vb/phrase.php
  • ./includes/functions_facebook.php
  • ./includes/functions_calendar.php
  • ./includes/functions_bigthree.php
  • ./includes/class_postbit.php
  • ./includes/class_bbcode.php
  • ./includes/functions_reputation.php
  • ./includes/functions_notice.php
  • ./packages/vbattach/attach.php
  • ./vb/types.php
  • ./vb/cache.php
  • ./vb/cache/db.php
  • ./vb/cache/observer/db.php
  • ./vb/cache/observer.php 

Hooks Called (72):
  • init_startup
  • friendlyurl_resolve_class
  • init_startup_session_setup_start
  • database_pre_fetch_array
  • database_post_fetch_array
  • init_startup_session_setup_complete
  • global_bootstrap_init_start
  • global_bootstrap_init_complete
  • cache_permissions
  • fetch_postinfo_query
  • fetch_postinfo
  • fetch_threadinfo_query
  • fetch_threadinfo
  • fetch_foruminfo
  • load_show_variables
  • load_forum_show_variables
  • global_state_check
  • global_bootstrap_complete
  • global_start
  • style_fetch
  • global_setup_complete
  • showthread_start
  • showthread_getinfo
  • strip_bbcode
  • friendlyurl_clean_fragment
  • friendlyurl_geturl
  • forumjump
  • cache_templates
  • cache_templates_process
  • template_register_var
  • template_render_output
  • fetch_template_start
  • fetch_template_complete
  • parse_templates
  • fetch_musername
  • notices_check_start
  • notices_noticebit
  • process_templates_complete
  • friendlyurl_redirect_canonical
  • showthread_post_start
  • showthread_query_postids
  • showthread_query
  • bbcode_fetch_tags
  • bbcode_create
  • showthread_postbit_create
  • postbit_factory
  • postbit_display_start
  • bbcode_parse_start
  • postbit_imicons
  • bbcode_parse_complete_precache
  • bbcode_parse_complete
  • postbit_display_complete
  • memberaction_dropdown
  • tag_fetchbit_complete
  • forumrules
  • navbits
  • navbits_complete
  • build_navigation_data
  • build_navigation_array
  • check_navigation_permission
  • process_navigation_links_start
  • process_navigation_links_complete
  • set_navigation_menu_element
  • build_navigation_menudata
  • build_navigation_listdata
  • build_navigation_list
  • set_navigation_tab_main
  • set_navigation_tab_fallback
  • navigation_tab_complete
  • fb_like_button
  • showthread_complete
  • page_templates