Replace non-efficient jQuery code with a while loop

Question

I have the following code working -

$('.sectionHeader:contains(Product Specific Documents)').next('div').find('table').find('input[type="checkbox"]').attr('checked', true);
var attr = $('.sectionHeader:contains(Product Specific Documents)').next('div').next('div').attr('id');
if(typeof attr !== undefined && attr !== false) {
$('.sectionHeader:contains(Product Specific Documents)').next('div').next('div').find('table').find('input[type="checkbox"]').attr('checked', true);
}

It basically selecting/checking checkboxes inside a specific table(s). It works fine but looks ugly.

I'd like to replace it with a while loop. The idea behind while loop is -

Find the required header (of table) and next DIV after that header is assigned to a variable. Then I check in a loop if id attribute exists and if yes, then I search for a table inside it then checkboxes inside and selecting them. Then I'm reassigning a variable adding next DIV and checking it in while loop.

So, the code looks like -

var at = $('.sectionHeader:contains(Product Specific Documents)').next('div');
while (typeof at.attr('id') !== undefined || at.attr('id') !== false) {
    at.find('table').find('input[type="checkbox"]').attr('checked', true);
    at = at.next('div');
}

But it doesn't work / it doesn't do the same as my initial code.

Answer 1

var at = $('.sectionHeader:contains(Product Specific Documents)').next('div');
for (var idx = 0; idx < 4 && (typeof at.attr('id') != 'undefined' && at.attr('id') != null); ++idx) {
    at.find('table').find('input[type="checkbox"]').attr('checked', true);
    at = at.next('div');
}

//This for loop works

I also found why while loop wasn't working - because the check for null was important -

var at = $('.sectionHeader:contains(Product Specific Documents)').next('div');
while (typeof at.attr('id') !== 'undefined' && at.attr('id') != null) {
    at.find('table').find('input[type="checkbox"]').attr('checked', true);
    at = at.next('div');
}

//This while also works