RJS: Check for existing page element?

问题

I have a textfield with the id "foo" that sometimes exists and sometimes not. If it exists I'd like to fill in a certain value.

How do you do this by using RJS (in Rails 2.2)?

I tried this and it doesn't work:

if page[:foo]
  page[:foo].value = "bar"
end

I get

TypeError: Null Value if the textfield doesn't exist

.

回答1:

I've come up on this many times where I have a conditional item that needs to be acted upon if it exists. Using page.select avoids the Null Value error.

  page.select('#dom_object_id').each do |element|
    element.value = "bar"
  end

I put this in my *.js.rjs file. When the select sends an empty array to each it returns nothing instead of the TypeError you'd get when directly selecting by id when no DOM object with the correct ID is on the page.

回答2:

I don't think you can from RJS. As a workaround, you can simply call a javascript method from RJS that checks if the element exists.

page << "update_foo('#{my_value}');"

Javascript ..

function update_foo(val)
{
  if( $('foo') != undefined )
  {
    $('foo').value = 'bar';
  } 
}

Edit

Fixed the ruby part..

来源：https://stackoverflow.com/questions/630637/rjs-check-for-existing-page-element