detecting line-breaks with jQuery?

is it possible to have jQuery/javascript detect where a string is broken (in order to fit into CSS width constraints) so as to insert DOM elements before the beginning of a new l开发者_如何学JAVAine?

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I came up with an approach, but it might be overkill for your purposes, so take this into account.

You need to create a clone of the element, empty the original, then move each word back into the original element. If the height changes at any point, there's a line-break before that word. This would be fairly simple to do using $(el).text(), but it gets more complicated if there can be other tags inside, not just text. I tried explaining how to break it down by node in this answer box, but found it easier just to create a jQuery plugin in a jsFiddle. Link here: http://jsfiddle.net/nathan/qkmse/ (Gist).

It won't handle floated elements all that well, and there are a few other situations where it'll fall over. Let me know if you'd like more options, or if it doesn't quite work for your purposes, or if you're not sure how to apply it and I'll try to help.

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Here is one approach. Note: I do not see a ideal solution without using monospace fonts. The equal with characters make this task much easier.

1. Equal width characters
2. Calculate the size of one character
3. Calculate the size of the container
4. Find characters per row
5. Find where the row will break (ie whitespace, dashes, etc)
6. Get all breaking indexes.

Have a look at the jsfiddle for associated html. I have not completed this function. More checks need to be put in when calculating the breaking index. Right now it is using lastIndexOf(' '), but this ignores that the next index could be a space, or the current. Also I am not accounting for other line-breaking characters. However this should be a great starting point.

var text = $('#text').text(),                   // "lorem ipsum ... "
    len = text.length,                          // total chars
    width = $('#text').width(),                 // container width
    span = $('<span />').append('a').appendTo('#sandbox'),
    charWidth = span.width(),                  // add single character to span and test width
    charsPerRow = Math.floor(width/charWidth); // total characters that can fit in one row

var breakingIndexes = [], // will contain indexes of all soft-breaks
    gRowStart = 0,        // global row start index
    gRowEnd = charsPerRow;// global row end index

while(gRowEnd < len){
    var rowEnd = text.substring(gRowStart, gRowEnd).lastIndexOf(' '); // add more checks for break conditions here
    breakingIndexes.push(gRowStart + rowEnd); // add breaking index to array
    gRowStart = gRowStart + rowEnd + 1; // next start is the next char
    gRowEnd = gRowStart + charsPerRow;  // global end inxex is start + charsperrow
}

var text2 = $('#text2').text();           // "lorem ipsum ... " now not width bound
var start = 0, newText = '';
for(var i=0; i < breakingIndexes.length; i++){
    newText += text2.substring(start, breakingIndexes[i]) + '<br />'; // add hard breaks
    start = breakingIndexes[i]; // update start
}

$('#text2').html(newText); // output with breaks

http://jsfiddle.net/Y5Ftn/1/

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this is my script, that takes text, and then makes each line a span

CSS:

    margin: 0;
        padding: 0;
    }

    .title{
        width: 300px;
        background-color: rgba(233,233,233,0.5);
        line-height: 20px;
    }

    span{
        color: white;
        background-color: red;
        display: inline-block;
        font-size: 30px;
    }

    a{
        text-decoration: none;
        color: black;
    }

html

<div class="title">
        <a href="">SOME TEXT LONG TEXT ANDTHISISLONG AND THIS OTHER TEXT</a>
    </div>

JS

$(function(){

        $(".title").find("a").each(function(){

            var $this = $(this);
            var originalText = $this.text();
            $this.empty();

            var sections = [];

            $.each( originalText.split(" "), function(){
                var $span = $("<span>" + this + "</span>");
                $this.append($span);

                var index = $span.position().top;

                if( sections[index] === undefined ){
                    sections[index] = "";
                }

                sections[index] += $span.text() + " ";
            });

            $this.empty();

            for(var i = 0; i< sections.length; i++){
                if( sections[i] !== undefined ){
                    var spanText = $.trim(sections[i]);                     
                    $this.append("<span>" + spanText + "</span>");
                }
            }

        });

    });

You have to got jQuery included.

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Alternatively you could compare width of the text block with its parent's width. If the block is at least 98% of the width of its parent, pretty sure it breaks

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I don't know of any built in jQuery of javascript function to do this. You could, however, do it yourself, but it would be potentially slow if you have a lot of text.

In theory, you could make sure the height is set to auto, remove the text, and then word by word reinsert it. On a change in the height, you remove the last word, and insert your dom element. Again, this will be slow if there is a lot of text, and the better way to do this would be to not change the original element, but do it in another element which could be hidden, and then replace the original element on completion. That way, your user wouldn't see the content disappear and then come back word by word.

Another way would be to use a similar principle, and start with an empty element of the same size with height auto, and insert a new character and a space until you get a new line. From there, you can use this as an approximation with the above techinique, or you can blindly add up the length of each string until you find a new line, taking into account the width of your dom element. This technique works better with monospaced fonts though, which is where using it only as an approximation comes in.

That said, there is a way to measure text using canvas, but that may be extreme. In theory it would be, create a canvas element, get the context, set all the font properties, and then use the context.measureText() method. An example of it use can be found here.

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Not sure what exactly your use case is but http://code.google.com/p/hyphenator/ may be a solution to your problem or if you dig into the hyphenator.js source code, you may be able to find the code you are looking for.

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I think it would be easier to detect using a regex -- much less code while retaining efficiency.

Here's something that worked for me:

if ((/(\r\n|\n|\r)/.test($(this).val()))) {
    alert('there are line breaks here')
}

I'm not sure if this will work with your broken strings, but it works for detecting line-breks with jQuery.