How to find absolute or relative position of text or in HTML?

Question

I was wondering if there is a way I could find the position of letters in HTML using Javascript or jQuery? I highly doubt this is possible, but it would make my life so much easier.

Alternatively, Is there a way to find the position of <br /> tags in HTML using JS?

Thanks in advance.

Answer 1

As tdammers mentions, handling all of the details of putting together a process to handle what you're suggesting has many nuances that may have to be addressed, depending on what you're doing.

The basics of what you're trying to do is:

1. Wrap an element around the text you want to find the position for, ie, in the case of text, probably a <span>.
2. Get either the $.offset() or $.position() of the element or elements you added. Whichever you choose is relevant to what you're trying to do; the first is relevant to the document, the second to the containing element.

I created a simple demo of a script to "highlight" a term typed into a textbox in several paragraphs using divs with position: absolute and top/left offsets relative to the terms found in the paragraphs (located by the <span> surrounding them).

Note, this is only a demonstration (of $.offset()); it's not production-ready code. There's a link to the live fiddle demo below the code snippets.

First, I created a function to find and create a highlight <div> for each term found.

function highlightWordPositions(word) {
    var $paras = $('p'),
        $spans,
        _top = 0,
        _left = 0;

    $paras.each(function(){
        var $p = $(this),
            regex = new RegExp(word, 'g');

        $p.html($p.text().replace(regex, '<span>' + word + '</span>'));
        $spans = $p.find('span');

        $spans.each(function(){
            var $span = $(this),
                $offset = $span.offset(),
                $overlay = $('<div class="overlay"/>');

            $overlay
                .offset($offset)
                .css({
                    width: $span.innerWidth(),
                    height: $span.innerHeight()
                }).show();

            $(document.body).append($overlay);
        });
    });
}

Then, I attached a callback to the $.keyup() event:

$('#term').keyup(function(event){
    var term = this.value;

    if (term == '') {
        $('.overlay').remove();
        return false;
    } else if (term.indexOf(' ') != -1) {
        this.value = term.replace(' ', '');
        return false;
    }

    $('.overlay').remove();

    highlightWordPositions(term);
});

http://jsfiddle.net/JaN75/

Answer 2

There is a simpler and more lightweight way (vs other answers that suggest overlays) to find the position of letters in DOM elements: use a range.

// returns { left, top, etc } in px
function getLetterPositions(myElementWithText, myTextElementIndex, myLetterPosition) {
    var range = document.createRange();
    range.setStart(myElementWithText.childNodes[myTextElementIndex], myLetterPosition);
    range.setEnd(myElementWithText.childNodes[myTextElementIndex], myLetterPosition+1);
    return range.getBoundingClientRect();
}

• the element with the text holding the target letter is myElementWithText (e.g. a <div>)
• the element child with the text (i.e. the textNode) is at index myTextElementIndex (in most cases, 0)
• the position of the letter you are trying to find is myLetterPosition (e.g. if text is "abcd" and you want "c", this will be 2)

Answer 3

Assuming that you mean the position where the character is displayed on screen, in pixels:

jQuery or the DOM do not model individual characters in their object models, so you can't read a character's position directly.

The best way I can think of is to insert a dummy element right before (or after) the character, e.g. a zero-width span with a special class, and then get its position. Alternatively, you can wrap the character in such a special element, and then get the wrapper's position, width, height, etc.

It's still not trivial, because you need to scan the HTML, and you don't want to break the HTML by inserting tags where they don't belong - for example, if you want to match the character 'd', you don't want to turn <div> into <<span class="magic">d</span>iv>, as that wouldn't be well-formed HTML.

Also, inserting those dummy elements may alter the layout slightly, depending on how the browser handles kerning.

Answer 4

in action: http://jsfiddle.net/WKgWM/

html:

<p>Percussus ait in fuerat construeret cena reges undis effugere quod una.</p>​

js:

var selection = "dis";
var spn = '<span class="selected">'+selection+'</span>';
$("p").html($("p").html().replace(selection,spn));

css:

.selected{
  background-color:#FF00FF;
}​