I have a question regarding using (what is to me) some complex XPath queries in Selenium IDE (thought they do apply to XPath in general).
Firstly, here is my scenario.
I'm writing some automated tests for a feature of a website I am working on that only certain items for sale on the website have. I'm trying to engineer the test in such a way that changes in data will not break it. Here is an abstraction of what I'm testing:
Given a set of search results, certain products within the results will have a feature (let's call the feature attributes), I want to click on the first result (which may change in the future) that has a single price and attributes.
I am using Selenium IDE 2.5.0 / FF 28.
Here is a JsFiddle I created that simulates the markup / DOM structure I have to work with (the markup cannot be changed): http://jsfiddle.net/xDaevax/3qUHB/6/
Here is my XPath query:
//div[contains(#class, 'primary')]//div[contains(#class, 'results')]//div[#class='price-range']/span[not(contains(#class, 'seperate'))]/../../..//a[#class='detail-link']
Essentially, the problem is this: All three have the same wrapping markup and css class information, but they differ in the price-range class due to the second element (the one I'm after) does not have "separate" or "minimum" CSS class elements.
I have made it this far with the XPath selector, but am stuck. I assume that when I traverse back up the DOM with the "/../..", I am losing the conditional XPath clause I previously used.
I apologize for the vagueness of the details, but due to contractual restrictions, I'm being as generic as possible.
Any suggestions on how to achieve the selection I want would be greatly appreciated. Please let me know if I need to clarify any of the requirements or steps I have tried.
Edit:
Here is a succinct description of the desired outcome.
In the markup example given, I want to select and click the link in the middle result element only. This is because the middle element has the desired "attributes" that once the link is clicked, it will take you to the product page which has additional things needing tested. That being said, the data could change: today it is the second element in the list, but maybe tomorrow it is the 7th element of 16 total elements.
My current logic for the XPath (though my solution does not work) is as follows: The element I am interested in is distinguishable from the other results because of two things: 1), it has a detail hyperlink (that will later be clicked) and 2) it does not have a range of prices (unlike the first result). Because the first result also has a hyperlink, the only difference between the two is that the first result has a minimum and separator markup element, while the second does not (my target link will always have a single price and not a range). Based on this information, I tried to write XPath that will select the first hyperlink that is not contained within an element that has a price range.
This expression will select all three div elements:
//div[contains(#class, 'primary')]
//div[contains(#class, 'results')]
//div[#class='price-range']
If I understood your requirements correctly, the price-range div must have a sibling that is an <a href> element, so we can filter out the last div by adding that restriction in a predicate: [../a[#href]]. So this expression selects only the first two divs:
//div[contains(#class, 'primary')]
//div[contains(#class, 'results')]
//div[#class='price-range']
[../a[#href]]
Now you can add one more predicate to remove the items that don't have a single price. You chose the separate class as the criterion, so we can change that last predicate and add another restriction to it: [../a[#href] and not(span[contains(#class,'separate')])]. Now your expression selects the div that you want:
//div[contains(#class, 'primary')]
//div[contains(#class, 'results')]
//div[#class='price-range']
[../a[#href] and not(span[contains(#class,'separate')])]
This is a location path, which creates a context. From this context, you can navigate anywhere you want. You can get the sibling <a href> adding a new step with its relative path: ../a. So, finally, this expression selects the link at the same level as your div:
//div[contains(#class, 'primary')]
//div[contains(#class, 'results')]
//div[#class='price-range']
[../a[#href] and not(span[contains(#class,'separate')])]
/../a
Or in one line:
//div[contains(#class, 'primary')]//div[contains(#class, 'results')]//div[#class='price-range'][../a[#href] and not(span[contains(#class,'separate')])]/../a
Related
I have a webpage with three <input> elements that all have the same name attribute. Ideally, I would like to select the second of these elements except sometimes there is only one element on the page and I want to instead select that element.
Ideally I would like something like (pseudo-code since max doesn't exist)
(//input[#name='myname'])[max(1, last()-1)]
I thought that maybe I could do something like the following except it yields all three elements
(//input[#name='myname'])[last()-1 or 1]
What is the best way to accomplish this using XPath?
Maybe grab both and then only the last one.
If there's two or more, it gets the second. If there's only one, it grabs that one.
((//input[#name='myname'])[position()=1 or position()=2])[last()]
This question already has answers here:
What is the difference between id and class in CSS, and when should I use them? [duplicate]
(15 answers)
Closed 8 years ago.
It looks like ids and classes are the exact same thing and have the same functionality, however ids are used just to show the coder/designer that they are only changing one item in those other similar items... Is that true?
I watched this helpful video http://www.youtube.com/watch?v=UZ4s1AvIDPM and that's the only difference I could tell.
It looks like ids and classes are the exact same thing and have the same functionality
Look again.
id specifically identifies an element. Each element can have no more than one id and each id must be unique throughout the DOM.
class describes an element in a more generic way, associating it logically with other elements of the same class. An element can have many classes, and the same class can be used many times throughout the DOM.
ids are used just to show the coder/designer that they are only changing one item in those other similar items... Is that true?
No, that's not true at all. ids uniquely identify (hence "id") elements. They can be used by a developer or a designer to target a specific element for some purpose (altering it, styling it, observing it, and so on).
The fact that the person is selecting an id does guarantee that they are targeting only one element (assuming that element exists, otherwise zero elements) as long as the document is well-formed (doesn't break the rule of not re-using id values, in which case the code is incorrect and behavior is undefined).
Conversely, when selecting based on a class value, any number of elements may be selected. So any developer and/or designer (or any other role) would bear that in mind and not assume that there's only one element.
Mootools slick selector engine documentation seems kind of sparse / unfriendly.
http://mootools.net/docs/core/Slick/Slick
An example:
Normally i can reach the last child of an element with:
$('wrapper').getLast().setStyle('background-color','green');
how do i utilize the new slick engine to achieve the same?
And where is the documentation?
Should i just learn CSS3 selectors?
In their example they use $$('p.foo !^') to get the last child of p class foo whatever that means. (do they mean the last instance of p.foo in the $$ array or the last child of the last element???)
Here i tried to fiddle a bit, the last two doesn't work:
http://jsfiddle.net/XLVr6/1/
The example bellow will select the last child of the element with id="wrapper. It will only return one element.
$$('#wrapper !^').setStyle('background-color','red');
or better way as only one element is needed, as it is faster:
document.getElement('#wrapper !^').setStyle('background-color','red');
However, if it's written like this where we select the last child of all p-elements on the page with class="wrapper"
$$('p.wrapper !^').setStyle('background-color','red');
Another way to do it is like this, however next example is faster:
('someId').getLast().setStyle('background-color','red');
As pointed out by Dimitar this is a better (faster) way to do it:
document.getElement('#someId :last-child')
As for your fiddle, the two last selectors should be written like this:
$$('#wrapper :last-child').setStyle('background-color','red');
$$('#wrapper !^').setStyle('background-color','red');
Please note the space between "wrapper" and ":last-child", that is because we are selecting the last child of a the child elements of "wrapper".
I want to access an element using a DOM hierarchy Node structure, through its parent nodes.I am trying to find the DOM hierarchy through firebug; want something like, <parent_node1>.<child_node1>.<child_node2> (not by document.getElementByID, getElementbyname) to access an element.
I want to automate a scenario like, I have column headers and corresponding values. Want to test, whether the values present under each column header, is correct...
I am thinking of using DOM as a method of automating this case...But, how can I find the DOM hierarchy...?
What I see through Inspect Element in Firebug is something like, list of events, elements and is not looking like a hierarchy node structure...Can somebody help in this regard please?
As discussed, you probably mean the DOM Element properties like element.childNodes, element.firstChild or similar.
Have a look at the DOM Element property reference over at JavaScriptKit, you'll get a good overview there how to access the hierarchy.
var currentTD = document.getElementsByTagName("td")[0];
var currentTable = document.getElementsByTagName("table")[0];
currentTD.parentNode // contains the TR element the TD resides in.
currentTable.childNodes // contains THEAD TBODY and TFOOT if present.
DOM Tables even have more properties like a rows collection and a cells collection.
A reminder of caution: Beware that these collections are live collections, so iterating over them and accessing collection.length in each iteration can be really slow because to get the length, the DOM has to be queried each time.
document.getElementById and document.getElementByTagname are using the DOM. They take an object within the DOM (specifically the document object, though you can also call both of those on elements) and return an object which is a single element or a collection of zero or more elements, respectively. That's a DOM operation. From there you can do other DOM operations on the results like getting children, parents or siblings, changing values etc.
All DOM operations come down to:
Take a starting point. This is often document though it's so often that the first thing we do is call document.getElementById or document.getElementByTagname and then work from the result that we could really consider that the starting point.
Find the element or elements we are interested in, relative to the starting point whether through startingPoint.getElementById* or startingPoing.getElementByTagname perhaps combined with some test (e.g. only working on those with a particular classname, if they have children of particular types, etc.
Read and/or change certain values, add new child nodes and/or delete nodes.
In a case like yours the starting point will be one or more tables found by document.getElementById(someID), document.getElementById(someID).getElementsByTagname('table')[0], or similar. From that table, myTable.getElementsByTagname('th') will get you the column headings. Depending on the structure, and what you are doing with it, you could just select corresponding elements from myTable.getElementsByTagname('td') or go through each row and then work on curRow.getElementsByTagname('td').
You could also just use firstChild, childNodes etc. though it's normally more convenient to have elements you don't care about filtered out by tagname.
*Since there can only be one element with a given id in a document, this will return the same if called on any element higher in the document hierarchy, so we normally just call this on document. It can be useful to call it on an element if we want to do something if the element is a descendant of our current element, and not otherwise.
CSS Selectors are matched by browser engines from right to left. So they first find the children and then check their parents to see if they match the rest of the parts of the rule.
Why is this?
Is it just because the spec says?
Does it affect the eventual layout if it was evaluated from left to right?
To me the simplest way to do it would be use the selectors with the least number of elements. So IDs first (as they should only return 1 element). Then maybe classes or an element that has the fewest number of nodes — e.g. there may only be one span on the page so go directly to that node with any rule that references a span.
Here are some links backing up my claims
http://code.google.com/speed/page-speed/docs/rendering.html
https://developer.mozilla.org/en/Writing_Efficient_CSS
It sounds like that it is done this way to avoid having to look at all the children of parent (which could be many) rather than all the parents of a child which must be one. Even if the DOM is deep it would only look at one node per level rather than multiple in the RTL matching. Is it easier/faster to evaluate CSS selectors LTR or RTL?
Keep in mind that when a browser is doing selector matching it has one element (the one it's trying to determine style for) and all your rules and their selectors and it needs to find which rules match the element. This is different from the usual jQuery thing, say, where you only have one selector and you need to find all the elements that match that selector.
If you only had one selector and only one element to compare against that selector, then left-to-right makes more sense in some cases. But that's decidedly not the browser's situation. The browser is trying to render Gmail or whatever and has the one <span> it's trying to style and the 10,000+ rules Gmail puts in its stylesheet (I'm not making that number up).
In particular, in the situation the browser is looking at most of the selectors it's considering don't match the element in question. So the problem becomes one of deciding that a selector doesn't match as fast as possible; if that requires a bit of extra work in the cases that do match you still win due to all the work you save in the cases that don't match.
If you start by just matching the rightmost part of the selector against your element, then chances are it won't match and you're done. If it does match, you have to do more work, but only proportional to your tree depth, which is not that big in most cases.
On the other hand, if you start by matching the leftmost part of the selector... what do you match it against? You have to start walking the DOM, looking for nodes that might match it. Just discovering that there's nothing matching that leftmost part might take a while.
So browsers match from the right; it gives an obvious starting point and lets you get rid of most of the candidate selectors very quickly. You can see some data at http://groups.google.com/group/mozilla.dev.tech.layout/browse_thread/thread/b185e455a0b3562a/7db34de545c17665 (though the notation is confusing), but the upshot is that for Gmail in particular two years ago, for 70% of the (rule, element) pairs you could decide that the rule does not match after just examining the tag/class/id parts of the rightmost selector for the rule. The corresponding number for Mozilla's pageload performance test suite was 72%. So it's really worth trying to get rid of those 2/3 of all rules as fast as you can and then only worry about matching the remaining 1/3.
Note also that there are other optimizations browsers already do to avoid even trying to match rules that definitely won't match. For example, if the rightmost selector has an id and that id doesn't match the element's id, then there will be no attempt to match that selector against that element at all in Gecko: the set of "selectors with IDs" that are attempted comes from a hashtable lookup on the element's ID. So this is 70% of the rules which have a pretty good chance of matching that still don't match after considering just the tag/class/id of the rightmost selector.
Right to left parsing, also called as bottom-up parsing is actually efficient for the browser.
Consider the following:
#menu ul li a { color: #00f; }
The browser first checks for a, then li, then ul, and then #menu.
This is because as the browser is scanning the page it just needs to look at the current element/node and all the previous nodes/elements that it has scanned.
The thing to note is that the browser starts processing moment it gets a complete tag/node and needn't have to wait for the whole page except when it finds a script, in which case it temporarily pauses and completes execution of the script and then goes forward.
If it does the other way round it will be inefficient because the browser found the element it was scanning on the first check, but was then forced to continue looking through the document for all the additional selectors. For this the browser needs to have the entire html and may need to scan the whole page before it starts css painting.
This is contrary to how most libs parse dom. There the dom is constructed and it doesn't need to scan the entire page just find the first element and then go on matching others inside it .
It allows for cascading from the more specific to the less specific. It also allows a short circuit in application. If the more specific rule applies in all aspects that the parent rule applies to, all parent rules are ignored. If there are other bits in the parent, they are applied.
If you went the other way around, you would format according to parent and then overwrite every time the child has something different. In the long run, this is a lot more work than ignoring items in rules that are already taken care of.