Javascript: Count visible characters in div

Question

I have a div which contains text (a string of length S) of an arbitrary length, but a fixed size. Beyond a certain length (let's call it L), the text is truncated and the remainder of the text is no longer visible. (Technically speaking, the range [0,L) is visible, the range [L,S) is not).

What I want to do is find the length L for the text by counting only the visible number of characters in the div. Any characters beyond the cut-off point should be disregarded.

I'm happy to use 3rd party libraries like jQuery etc if that will get the job done!

Answer 1

Here is a function I made for trimming text:

function getTextThatFits(txt, w, fSize, fName, fWeight) {
    if (fWeight === undefined)
        fWeight = "normal";

    var auxDiv = $("<div>").addClass("auxdiv").css ({
        fontFamily : fName,
        fontSize : parseInt(fSize) + "px",
        position: "absolute",
        height: "auto",
        marginLeft : "-1000px",
        marginTop : "-1000px",
        fontWeight: fWeight,
        width: "auto"
    })
    .appendTo($("body"))
    .html(txt);

    var ww = (auxDiv.width() + 1);
    var str = txt;

    if (ww > w)
    {
        var i = 1, p = 1, u = txt.length, sol = 0;

        while (p <= u)
        {
            i = (p + u) >> 1;
            str = txt.slice(0, i);
            auxDiv.html(str);
            ww = (auxDiv.width() + 1);
            if (ww <= w) {
                sol = i;
                p = i + 1;
            }
            else u = i - 1;
        }

        str = txt.slice(0, sol);
    }
    $(".auxdiv").remove();
    auxDiv.remove();
    return str.length;
}

I'm using binary search for finding the text that fits into a specific width. In order to use the function, you must call it like this:

getTextThatFits(yourText, divWidth, fontSize, fontName, fontWeight=optional)