请告知我可以进行的任何改进.

http://jsfiddle.net/zQUhV/47/

我所做的是通过每个工作拆分段落,逐个将它们插入一个新元素,检查高度变化 – 当它改变时,添加了一个新行.

此函数返回包含行文本,起始索引和结束索引的行对象数组：

(function($) {
$.fn.lines = function(){
    words = this.text().split(" "); //split text into each word
    lines = [];
 
    hiddenElement = this.clone(); //copies font settings and width
    hiddenElement.empty();//clear text
    hiddenElement.css("visibility","hidden");
 
    jQuery('body').append(hiddenElement); // height doesn't exist until inserted into document
 
    hiddenElement.text('i'); //add character to get height
    height = hiddenElement.height();
    hiddenElement.empty();
 
    startIndex = -1; // quick fix for now - offset by one to get the line indexes working
    jQuery.each(words,function() {
      lineText = hiddenElement.text(); // get text before new word appended
      hiddenElement.text(lineText + " " + this);
        if(hiddenElement.height() > height) { // if new line
            lines.push({text: lineText,startIndex: startIndex,endIndex: (lineText.length + startIndex)}); // push lineText not hiddenElement.text() other wise each line will have 1 word too many
            startIndex = startIndex + lineText.length +1;
            hiddenElement.text(this); //first word of the next line
        }
   });
    lines.push({text: hiddenElement.text(),endIndex: (hiddenElement.text().length + startIndex)}); // push last line
    hiddenElement.remove();
    lines[0].startIndex = 0; //quick fix for now - adjust first line index
    return lines;
}
})(jQuery);

现在,您可以使用它来测量直到光标点的字符数,并在遍历段落时应用该字符以保持光标相对于行的开头的位置.然而,当将’i’的宽度考虑为’m’的宽度时,这会产生非常不准确的结果.

相反,最好找到直到光标点的直线宽度：

function distanceToCaret(textElement,caretIndex){
 
    line = findLineViaCaret(textElement,caretIndex);
    if(line.startIndex == 0) { 
     // +1 needed for substring to be correct but only first line?
        relativeIndex = caretIndex - line.startIndex +1;
    } else {
      relativeIndex = caretIndex - line.startIndex;  
    }
    textToCaret = line.text.substring(0,relativeIndex);
 
    hiddenElement = textElement.clone(); //copies font settings and width
    hiddenElement.empty();//clear text
    hiddenElement.css("visibility","hidden");
    hiddenElement.css("width","auto"); //so width can be measured
    hiddenElement.css("display","inline-block"); //so width can be measured
 
    jQuery('body').append(hiddenElement); // doesn't exist until inserted into document
 
    hiddenElement.text(textToCaret); //add to get width
    width = hiddenElement.width();
    hiddenElement.remove();
 
    return width;
}
function findLineViaCaret(textElement,caretIndex){
    jQuery.each(textElement.lines(),function() {
        if(this.startIndex <= caretIndex && this.endIndex >= caretIndex) {
            r = this;
            return false; // exits loop
        }
   });
    return r;
}

然后将目标线分割成字符,并通过逐个添加字符找到最接近上面宽度的点,直到达到该点：

function getCaretViaWidth(textElement,lineNo,width) {
    line = textElement.lines()[lineNo-1];
 
    lineCharacters = line.text.replace(/^\s+|\s+$/g,'').split("");
 
    hiddenElement = textElement.clone(); //copies font settings and width
    hiddenElement.empty();//clear text
    hiddenElement.css("visibility","inline-block"); //so width can be measured
 
    jQuery('body').append(hiddenElement); // doesn't exist until inserted into document
 
    if(width == 0) { //if width is 0 index is at start
        caretIndex = line.startIndex;
    } else {// else loop through each character until width is reached
        hiddenElement.empty();
        jQuery.each(lineCharacters,function() {
            text = hiddenElement.text();
            prevWidth = hiddenElement.width();
            hiddenElement.text(text + this);
            elWidth = hiddenElement.width();
            caretIndex = hiddenElement.text().length + line.startIndex;
            if(hiddenElement.width() > width) {
                // check whether character after width or before width is closest
                if(Math.abs(width - prevWidth) < Math.abs(width - elWidth)) {
                   caretIndex = caretIndex -1; // move index back one if prevIoUs is closes
                }
                return false;
            }
        });
    }
    hiddenElement.remove();
    return caretIndex;
}

使用以下keydown函数足以在令人满意的段落之间准确遍历：

$(document).on('keydown','p[contenteditable="true"]',function(e) {
    //if cursor on first line & up arrow key
    if(e.which == 38 && (cursorIndex() < $(this).lines()[0].text.length)) { 
        e.preventDefault();
        if ($(this).prev().is('p')) {
            prev = $(this).prev('p');
            getDistanceToCaret = distanceToCaret($(this),cursorIndex());
            lineNumber = prev.lines().length;
            caretPosition = getCaretViaWidth(prev,lineNumber,getDistanceToCaret);
            prev.focus();
            setCaret(prev.get(0),caretPosition);
        }
    // if cursor on last line & down arrow
    } else if(e.which == 40 && cursorIndex() >= $(this).lastLine().startIndex && cursorIndex() <= ($(this).lastLine().startIndex + $(this).lastLine().text.length)) {
        e.preventDefault();
        if ($(this).next().is('p')) {
            next = $(this).next('p');
            getDistanceToCaret = distanceToCaret($(this),cursorIndex());
            caretPosition = getCaretViaWidth(next,1,getDistanceToCaret);
            next.focus();
            setCaret(next.get(0),caretPosition);
        }
        //if start of paragraph and left arrow
    } else if(e.which == 37 && cursorIndex() == 0) {
        e.preventDefault();
        if ($(this).prev().is('p')) {
            prev = $(this).prev('p');
            prev.focus();
            setCaret(prev.get(0),prev.text().length); 
        }
        // if end of paragraph and right arrow
    } else if(e.which == 39 && cursorIndex() == $(this).text().length) {
        e.preventDefault();
        if ($(this).next().is('p')) {
            $(this).next('p').focus();
        }
    };