jquery - Masterpage javascript causes an object reference error when asp.net control doesn't exist in the content page -

so here's deal: have asp.net control located on content pages not others. reference asp.net control within $(document).click event, code located in master page. code below how went doing that; searches contentplaceholder "body" control "dep_ddb" , retrieves client id.

var dep_ddb = document.getelementbyid('<%= body.findcontrol("dep_ddb").clientid %>'); var filterbutton = document.getelementbyid('<%=body.findcontrol("filterbutton").clientid %>'); 

this works great when loading page includes control. unfortunately, when loading page doesn't use control uses master page, object reference error on vb code: <%= blah blah %>.

i tried using javascript if statement detect if content page doesn't include control (simply using title check if dealing content page know won't include control):

if (ttl.indexof('| sign up') == -1) {     var dep_ddb = document.getelementbyid('<%= body.findcontrol("dep_ddb").clientid %>');     var filterbutton = document.getelementbyid('<%=body.findcontrol("filterbutton").clientid %>'); }; 

. . . still caused object reference error. believe asp trying compile code included in <% %> tags first, , returning error since doesn't exist. mean there no javascript-based "if statement" can use omit code when necessary.

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so question this:

what method can used safely reference asp.net control master page when control exists in content page, , omit reference when not exist?

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please both of below links. may you'll help:

check if element exists in jquery

is there "exists" function jquery?

one more thing, instead of using body.findcontrol("dep_ddb").clientid try give direct client id getting page source. won't show server error.