Question

Please forgive me if I repeat the question.

I have HTML　that all elements inside a div tag has different id, suppose I have already get the reference to the div, is there any simple way to get the element by its id without iterate all elements with that div?

here is my sample html:

<div id="div1" >
    <input type="text" id="edit1" />
    <input type="text" id="edit2" />
</div>
<div id="div2" >
    <input type="text" id="edit1" />
    <input type="text" id="edit2" />
</div>

Answer 1

You may try something like this.

Sample Markup.

<div id="div1" >
    <input type="text" id="edit1" />
    <input type="text" id="edit2" />
</div>
<div id="div2" >
    <input type="text" id="edit3" />
    <input type="text" id="edit4" />
</div>

JavaScript

function GetElementInsideContainer(containerID, childID) {
    var elm = {};
    var elms = document.getElementById(containerID).getElementsByTagName("*");
    for (var i = 0; i < elms.length; i++) {
        if (elms[i].id === childID) {
            elm = elms[i];
            break;
        }
    }
    return elm;
}

Demo: http://jsfiddle.net/naveen/H8j2A/

A better method as suggested by nnnnnn

function GetElementInsideContainer(containerID, childID) {
    var elm = document.getElementById(childID);
    var parent = elm ? elm.parentNode : {};
    return (parent.id && parent.id === containerID) ? elm : {};
}

Demo: http://jsfiddle.net/naveen/4JMgF/

Call it like

var e = GetElementInsideContainer("div1", "edit1");