using maskededitextender in javascript

i have a AjaxControlToolkit.MaskedEditExtender targeted to a text control for accepting date

i have the code for the same in code behind page

as

Dim Extender As AjaxControlToolkit.MaskedEditExtender
Extender = CType(e.Row.FindControl("MASK"), AjaxControlToolkit.MaskedEditExtender)
Extender.TargetControlID = "txtRemrk"

how do i do the same in javascript