在document.ready中设置隐藏字段的值，并在pageload事件中获取其值

Question

I am trying to set hidden fied value in document.ready function and get it in PageLoad event but its value always empty where I am wrong please suggest me. My javascript code is

    $(document).ready(function () {
        if (document.getElementById('<%=hdnMiddlediv.ClientID %>').value = '')
        { document.getElementById('<%=hdnMiddlediv.ClientID %>').value = 'test'; }
    });
</script>

c#

    protected void Page_Load(object sender, EventArgs e)
    {
        string val = hdnMiddlediv.Value;
        if (!IsPostBack)
        {
            string val2 = hdnMiddlediv.Value;

        }
    }

Answer 1

Use Comparision(==/===) operator instead of Assignment(=) operator. If you use assignment operator, the condition will always evaluate to false and your code inside if will never execute.

if (document.getElementById('<%=hdnMiddlediv.ClientID %>').value == '')
//                                                               ^^

If you're using jQuery use val() to get/set value of an element:

$(document).ready(function() {
    if ($('#<%=hdnMiddlediv.ClientID %>').val()) {
        $('#<%=hdnMiddlediv.ClientID %>').val('test');
    }
});