Comparing boundary points between ranges

Question

I don't know if the title is right. The thing is that I have found a snippet to get the cursor position when it's focused in a contenteditable element. I understand the whole code, but there are five lines that I do no t know for what they are good.

Ok. This lines are a function, which is passed to a Treewalker as a parameter. And they deal with comparing boundary points, but, how, and for what?. I have been researching lot of days, and haven't found ists functionality yet.

function(node) {
        var nodeRange = document.createRange();
        nodeRange.selectNode(node);
        return nodeRange.compareBoundaryPoints(Range.END_TO_END, range) < 1 ?
            NodeFilter.FILTER_ACCEPT : NodeFilter.FILTER_REJECT;
    }

The whole snippet is this (just to situate it in context):

function getCharacterOffsetWithin(range, node) {
var treeWalker = document.createTreeWalker(
    node,
    NodeFilter.SHOW_TEXT,
    function(node) {
        var nodeRange = document.createRange();
        nodeRange.selectNode(node);
        return nodeRange.compareBoundaryPoints(Range.END_TO_END, range) < 1 ?
            NodeFilter.FILTER_ACCEPT : NodeFilter.FILTER_REJECT;
    },
    false
);

var charCount = 0;
while (treeWalker.nextNode()) {
    charCount += treeWalker.currentNode.length;
}
if (range.startContainer.nodeType == 3) {
    charCount += range.startOffset;
}
return charCount;
}

document.body.addEventListener("keyup", function() {
  var el = document.getElementById("test");
  var range = window.getSelection().getRangeAt(0);
  document.getElementById("position").innerHTML = "Caret char pos: " + getCharacterOffsetWithin(range, el);
}, false);

It can be seen on work here: JS Fiddle

Thank you a lot, I just want to understand this stuff before working with it. Sorry for the long Post.

score 2 · Accepted Answer · edited May 23 '17 at 10:34

2

This looks like my code, from this question. It's overly complicated for the task it's trying to accomplish and I provided a simpler alternative to a similar question that I would recommend using instead. I've now updated the original answer with a link to the simpler answer.

As to your question about what that function does, it's there to filter nodes. The TreeWalker visits all text nodes within the container node and yields only nodes those that are located before the end of the selection. The filter function is called on each text node, creates a range encompassing the text node and checks whether the end of the text node is earlier in the document than the end of the selection range using compareBoundaryPoints().

edited May 23 '17 at 10:34

Community

1
1

answered Jun 14 '12 at 09:34

Tim Down

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Ok... thank you a lot for the answer. It is really complet... I still have some questions, after researching about some things: in getRangeAt(index)... does the index mean "range number"?... for example, if user does two or more selections... in order to usually get the first one, index=0? – Kenedy Jun 14 '12 at 11:33
And on the other hand... when it checks if selection type is "Control"... I know there are three types, but this one i don't know what it means... (when the user makes multiple selections, maybe?) – Kenedy Jun 14 '12 at 11:43
That's an IE thing. Within an editable element, clicking on an object like a table or an image or an input shows resize handles. When that happens, the selection is of type "Control". IE optionally allows multiple elements to be selected this way. – Tim Down Jun 14 '12 at 11:50

Comparing boundary points between ranges

1 Answers1