How to find text box value inside of grid view using javascript

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how to find textbox value inside of gridview using javascript
i am trying this way but it does not response

What I have tried:

<asp:gridview>
<asp:TextBox ID="txtProductId" runat="server" text='<%# Container.DataItem("Productid")%>'  ></asp:TextBox>
<asp:gridView>

function showGrid()
{
var pid = $(row).find("input[id*=txtProductId]").text();
}