Question

I want to do a javascript function that check the unchecked checkbox. My function nowadays, check all the unchecked checkbox, and I need that just check a specific GridView unchecked checkbox

function checar() {    
    var el = document.getElementsByTagName("input");
    for (var i = 0; i < el.length; i++) {
        if (el[i].type == "checkbox") {
            el[i].checked = true;
        }
    }
}

Answer 1

You want to first limit the scope of your search for elements. One way to do so would be to use getElementById

function checar() { 
var grd = document.getElementById("<%=grd.ClientID%>"); // <-- Add this line
var el = grd.getElementsByTagName("input"); // <-- change the scope of this to grd
//rest of your code here.
}

Sample using divs, but you’ll get the idea I think: http://jsfiddle.net/8LRkk/

Edited to include setting the specific Grid ID.