在HTML中获取段落的一行

Question

在JavaScript中,是否可以从页面上显示的段落中获取特定行？

例如,在这里我试图获取段落的第3行作为字符串:

JavaScript的:

//this function should return the specified line from the specified paragraph.
function getLine(paragraphId, lineNum){
    //for example, getLine("sampleParagraph", 1); should return
    // tore but year. An from mean on with when sing pain. Oh to as principles devonshire
}

HTML:

<p id = "sampleParagraph">
Instrument cultivated alteration any favourable expression law far nor. Both new like tore but year. An from mean on with when sing pain. Oh to as principles devonshire companions unsatiable an delightful. The ourselves suffering the sincerity. Inhabit her manners adapted age certain. Debating offended at branched striking be subjects.
</p>

这里是jsfiddle(显示段落的显示方式):http://jsfiddle.net/RrXWW/

Answer 1

演示1: http ://jsfiddle.net/LeTW6/2/
演示2: http ://jsfiddle.net/LeTW6/3/

我在这里使用jQuery是为了简单,但这适用于纯JavaScript.实际上,我在某些部分使用直接DOM访问来提高性能.

1. 将所有单词分成单独的元素.
2. 使用位置计算行号.
3. 在选定的行中,开始构建所有单词元素的缓冲区.
4. 大于所选行,退出.
5. 调整大小时,重新计算(可能不需要,也可能从其他事件调用).

码

(function () {

    // wrap all words
    $(".count").each(function () {
        var obj = $(this);
        var html = obj.html().replace(/(\S+\s*)/g, "<span>$1</span>");
        obj.html(html);
    });

    var offset = 0; // keeps track of distance from top
    var spans = $(".count span"); // collection of elements

    function getLine(index) {
        var top = 0,
            buffer = [];

        for (var i = 0; i < spans.length; i++) {

            if (top > index) {
                break; // quit once the line is done to improve performance
            }

            // position calculation
            var newOffset = spans[i].offsetTop;
            if (newOffset !== offset) {
                offset = newOffset;
                top++;
            }

            // store the elements in the line we want
            if (top === index) {
                buffer.push(spans[i]);
            }
        }

        // buffer now contains all spans in the X line position

        // this block is just for output purposes
        var text = "";
        for (var i = 0; i < buffer.length; i++) {
            text += buffer[i].innerHTML;
        }

        $("#output").html(text);
    }

    var line = 3; // the line to select/highlight
    getLine(line); // initial highlighting

    // other recalculation triggers can be added here, such as a button click

    // throttling to handle recalculation upon resize
    var timeout;
    function throttle() {
        window.clearTimeout(timeout);
        timeout = window.setTimeout(function () {
            getLine(line);
        }, 100);
    }

    $(window).on("resize", throttle);
})();

另请参阅我的答案,突出显示可变宽度容器中的备用行.

Answer 2

如果您想使用纯 JavaScript 来提高性能并且不必包含 jQuery，则可以使用它。

演示： http: //jsfiddle.net/PX7cj/2/

function getLine(paragraphId, lineNum) {
    lineNum--;
    var elem = document.getElementById(paragraphId);
    var spanChildren = elem.getElementsByTagName("span");
    var paragraphText = elem.innerHTML.replace(/(\r\n|\n|\r)/gm, "");
    var newParagraphText = "";
    var words = [];
    if (spanChildren.length === 0) {
        words = paragraphText.split(" ");
        for (var i = 0; max = words.length, i < max; i++)
        newParagraphText += '<span>' + words[i] + "</span> ";
        elem.innerHTML = newParagraphText;
    }else{
        for(var i=0; max = spanChildren.length, i<max; i++){
            words[words.length] = spanChildren[i].innerHTML;
        }
    }
    var lineCounter = 0;
    var previousY = spanChildren[0].offsetTop;
    var returnText = "";
    var startReturning = false;
    for (var i = 0; max = words.length, i < max; i++) {
        if (spanChildren[i].offsetTop != previousY) lineCounter++;
        if (lineCounter === lineNum) startReturning = true;
        if (lineCounter !== lineNum && startReturning) return returnText.substring(0, returnText.length - 1);
        if (startReturning) {
            returnText += words[i] + " ";
            if (i + 1 === words.length) return returnText.substring(0, returnText.length - 1);
        }
        previousY = spanChildren[i].offsetTop;
    }
}

alert(getLine("sampleParagraph", 5));
alert(getLine("sampleParagraph", 4));