很好地截断一个字符串以适合给定的像素宽度

Question

有时你的字符串必须符合某个像素宽度.此功能尝试有效地执行此操作.请在下面发布您的建议或重构:)

function fitStringToSize(str,len) {
    var shortStr = str;
    var f = document.createElement("span");
    f.style.display = 'hidden';
    f.style.padding = '0px';
    document.body.appendChild(f);

    // on first run, check if string fits into the length already.
    f.innerHTML = str;
    diff = f.offsetWidth - len;

    // if string is too long, shorten it by the approximate 
    // difference in characters (to make for fewer iterations). 
    while(diff > 0)
    {
        shortStr = substring(str,0,(str.length - Math.ceil(diff / 5))) + '…';
        f.innerHTML = shortStr;
        diff = f.offsetWidth - len;
    }

    while(f.lastChild) {
        f.removeChild(f.lastChild);
    }
    document.body.removeChild(f);

    // if the string was too long, put the original string 
    // in the title element of the abbr, and append an ellipsis
    if(shortStr.length < str.length)
    {
        return '<abbr title="' + str + '">' + shortStr + '</abbr>';
    }
    // if the string was short enough in the first place, just return it.
    else
    {
        return str;
    }
}

更新:@下面的某些解决方案要好得多; 请使用它.

更新2:代码现在作为要点发布; 随意分叉并提交补丁:)

Answer 1

您的代码存在一些问题.

• 为什么/ 5？字符的宽度取决于font-family和font-size.
• 你必须str在abbr标题中逃避(否则"将使代码无效).
• diff 未声明并最终在全局范围内
• 本substring是不应该这样的工作.你使用的是什么浏览器？
• hidden不是有效值style.display.要隐藏它,您应该使用该值,none但浏览器不会计算offsetWidth.请style.visibility="hidden"改用.
• 寻找合适的长度是非常低效的.
• 必须逃避</abbr>"

我为你重写了它并添加了className所以你可以使用一个样式来设置font-family和font-size.Fooz先生建议您使用鼠标悬停来显示整个字符串.这是没有必要的,因为现代浏览器为您做到这一点(使用FF,IE,Opera和Chrome测试)

    function fitStringToSize(str,len,className) {
    var result = str; // set the result to the whole string as default
    var span = document.createElement("span");
    span.className=className; //Allow a classname to be set to get the right font-size.
    span.style.visibility = 'hidden';
    span.style.padding = '0px';
    document.body.appendChild(span);


    // check if the string don't fit 
    span.innerHTML = result;
    if (span.offsetWidth > len) {
        var posStart = 0, posMid, posEnd = str.length;
        while (true) {
            // Calculate the middle position
            posMid = posStart + Math.ceil((posEnd - posStart) / 2);
            // Break the loop if this is the last round
            if (posMid==posEnd || posMid==posStart) break;

            span.innerHTML = str.substring(0,posMid) + '…';

            // Test if the width at the middle position is
            // too wide (set new end) or too narrow (set new start).
            if ( span.offsetWidth > len ) posEnd = posMid; else posStart=posMid;
        }
        //Escape
        var title = str.replace("\"",""");
        //Escape < and >
        var body = str.substring(0,posStart).replace("<","&lt;").replace(">","&gt;");
        result = '<abbr title="' + title + '">' + body + '&hellip;<\/abbr>';
    }
    document.body.removeChild(span);
    return result;
    }

编辑:在测试更多时,我发现了一些错误.

• 我用Math.ceil而不是预期的Math.floor(我责备这个,因为英语不是我的母语)

• 如果输入字符串有html-tags,那么结果将是未定义的(在中间截断标记或保留开放标记是不好的)

改进:

• 转义复制到所有位置的范围的字符串.您仍然可以使用html-entities,但不允许使用任何标签(<并将>显示)
• while重写了-statement(它更快一点,但主要原因是摆脱导致额外轮次并摆脱破坏声明的错误)
• 将功能重命名为 fitStringToWidth

版本2:

function fitStringToWidth(str,width,className) {
  // str    A string where html-entities are allowed but no tags.
  // width  The maximum allowed width in pixels
  // className  A CSS class name with the desired font-name and font-size. (optional)
  // ----
  // _escTag is a helper to escape 'less than' and 'greater than'
  function _escTag(s){ return s.replace("<","&lt;").replace(">","&gt;");}

  //Create a span element that will be used to get the width
  var span = document.createElement("span");
  //Allow a classname to be set to get the right font-size.
  if (className) span.className=className;
  span.style.display='inline';
  span.style.visibility = 'hidden';
  span.style.padding = '0px';
  document.body.appendChild(span);

  var result = _escTag(str); // default to the whole string
  span.innerHTML = result;
  // Check if the string will fit in the allowed width. NOTE: if the width
  // can't be determined (offsetWidth==0) the whole string will be returned.
  if (span.offsetWidth > width) {
    var posStart = 0, posMid, posEnd = str.length, posLength;
    // Calculate (posEnd - posStart) integer division by 2 and
    // assign it to posLength. Repeat until posLength is zero.
    while (posLength = (posEnd - posStart) >> 1) {
      posMid = posStart + posLength;
      //Get the string from the beginning up to posMid;
      span.innerHTML = _escTag(str.substring(0,posMid)) + '&hellip;';

      // Check if the current width is too wide (set new end)
      // or too narrow (set new start)
      if ( span.offsetWidth > width ) posEnd = posMid; else posStart=posMid;
    }

    result = '<abbr title="' +
      str.replace("\"","&quot;") + '">' +
      _escTag(str.substring(0,posStart)) +
      '&hellip;<\/abbr>';
  }
  document.body.removeChild(span);
  return result;
}