By Default Javascript Is Calling At The Time Of Pageload(),How Do I Stop It?

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Javascript

i have one javascript file & product page

<div class="preview" style=" background:#ffffff;">
                   <center>
                    
                    <asp:ImageButton ID="imgSuryaCem" runat="server" ImageUrl="images/Images/White-Limewash.gif" style="max-height:200px; vertical-align:middle; flex-item-align:center; flex-align:center; background-position:center; " OnClientClick="lightbox_open();" />
                 </center>
                    <div id="light" onclick="lightbox_close();">
                        <a>CLOSE(X)</a><img id="imgSuryaCem1" alt=" " src="images/Big/White_Limewash.gif"  style=" vertical-align:middle; flex-item-align:center; flex-align:center; background-position:center; " />
                    </div>
                </div>

at the time of page load also java-script is executing..Please give me the solution.