如何使用JavaScript查找INPUT和TEXTAREA Caret位置坐标

经过不断的努力和尝试，我找到了我想要的答案，我在下面以代码的形式分享它，您可以在https://jsfiddle.net/qjkkqdg2/1/而且

<script type="text/javascript">
/* Main Function
----------------------------------------------- */
function myFunction(Desired_ID){
    // Extra Codes Here ETC...
    document.getElementById(Desired_ID.id).style.backgroundColor = "red";
    // Extra Codes Here ETC...
    var coordinates = getCaretCoordinates(Desired_ID, Desired_ID.selectionStart);
    alert(coordinates.left + ", " + coordinates.top);
    // Extra Codes Here ETC...
}
/* Get Caret XY Coordinate
----------------------------------------------- */
/* jshint browser: true */
(function () {
// The properties that we copy into a mirrored div.
// Note that some browsers, such as Firefox,
// do not concatenate properties, i.e. padding-top, bottom etc. -> padding,
// so we have to do every single property specifically.
var properties = [
  'direction',  // RTL support
  'boxSizing',
  'width',  // on Chrome and IE, exclude the scrollbar, so the mirror div wraps exactly as the textarea does
  'height',
  'overflowX',
  'overflowY',  // copy the scrollbar for IE
  'borderTopWidth',
  'borderRightWidth',
  'borderBottomWidth',
  'borderLeftWidth',
  'borderStyle',
  'paddingTop',
  'paddingRight',
  'paddingBottom',
  'paddingLeft',
  // https://developer.mozilla.org/en-US/docs/Web/CSS/font
  'fontStyle',
  'fontVariant',
  'fontWeight',
  'fontStretch',
  'fontSize',
  'fontSizeAdjust',
  'lineHeight',
  'fontFamily',
  'textAlign',
  'textTransform',
  'textIndent',
  'textDecoration',  // might not make a difference, but better be safe
  'letterSpacing',
  'wordSpacing',
  'tabSize',
  'MozTabSize'
];
var isBrowser = (typeof window !== 'undefined');
var isFirefox = (isBrowser && window.mozInnerScreenX != null);
function getCaretCoordinates(element, position, options) {
  if(!isBrowser) {
    throw new Error('textarea-caret-position#getCaretCoordinates should only be called in a browser');
  }
  var debug = options && options.debug || false;
  if (debug) {
    var el = document.querySelector('#input-textarea-caret-position-mirror-div');
    if ( el ) { el.parentNode.removeChild(el); }
  }
  // mirrored div
  var div = document.createElement('div');
  div.id = 'input-textarea-caret-position-mirror-div';
  document.body.appendChild(div);
  var style = div.style;
  var computed = window.getComputedStyle? getComputedStyle(element) : element.currentStyle;  // currentStyle for IE < 9
  // default textarea styles
  style.whiteSpace = 'pre-wrap';
  if (element.nodeName !== 'INPUT')
    style.wordWrap = 'break-word';  // only for textarea-s
  // position off-screen
  style.position = 'absolute';  // required to return coordinates properly
  if (!debug)
    style.visibility = 'hidden';  // not 'display: none' because we want rendering
  // transfer the element's properties to the div
  properties.forEach(function (prop) {
    style[prop] = computed[prop];
  });
  if (isFirefox) {
    // Firefox lies about the overflow property for textareas: https://bugzilla.mozilla.org/show_bug.cgi?id=984275
    if (element.scrollHeight > parseInt(computed.height))
      style.overflowY = 'scroll';
  } else {
    style.overflow = 'hidden';  // for Chrome to not render a scrollbar; IE keeps overflowY = 'scroll'
  }
  div.textContent = element.value.substring(0, position);
  // the second special handling for input type="text" vs textarea: spaces need to be replaced with non-breaking spaces - http://stackoverflow.com/a/13402035/1269037
  if (element.nodeName === 'INPUT')
    div.textContent = div.textContent.replace(/'s/g, ''u00a0');
  var span = document.createElement('span');
  // Wrapping must be replicated *exactly*, including when a long word gets
  // onto the next line, with whitespace at the end of the line before (#7).
  // The  *only* reliable way to do that is to copy the *entire* rest of the
  // textarea's content into the <span> created at the caret position.
  // for inputs, just '.' would be enough, but why bother?
  span.textContent = element.value.substring(position) || '.';  // || because a completely empty faux span doesn't render at all
  div.appendChild(span);
  var coordinates = {
    top: span.offsetTop + parseInt(computed['borderTopWidth']),
    left: span.offsetLeft + parseInt(computed['borderLeftWidth'])
  };
  if (debug) {
    span.style.backgroundColor = '#aaa';
  } else {
    document.body.removeChild(div);
  }
  return coordinates;
}
if (typeof module != 'undefined' && typeof module.exports != 'undefined') {
  module.exports = getCaretCoordinates;
} else if(isBrowser){
  window.getCaretCoordinates = getCaretCoordinates;
}
}());
</script>

这个id代码https://github.com/component/textarea-caret-position.谢谢他。。。

限制：

它只给出了关于元素的坐标，但我想得到它关于整个文档的坐标。。。

为了解决这个限制，我添加了另一个函数，它将查找元素相对于整个文档的坐标，所以只需添加下面的函数。。。

<script type="text/javascript">
/* Get Element XY Coordinate
----------------------------------------------- */
function getElementCoords(elem) { // crossbrowser version
    var box = elem.getBoundingClientRect();
    var body = document.body;
    var docEl = document.documentElement;
    var scrollTop = window.pageYOffset || docEl.scrollTop || body.scrollTop;
    var scrollLeft = window.pageXOffset || docEl.scrollLeft || body.scrollLeft;
    var clientTop = docEl.clientTop || body.clientTop || 0;
    var clientLeft = docEl.clientLeft || body.clientLeft || 0;
    var top  = box.top +  scrollTop - clientTop;
    var left = box.left + scrollLeft - clientLeft;
    return { top: Math.round(top), left: Math.round(left) };
}
</script>

因此，我们的主要功能现在将是…

<script type="text/javascript">
/* Main Function
----------------------------------------------- */
function myFunction(Desired_ID){
    // Extra Codes Here ETC...
    document.getElementById(Desired_ID.id).style.backgroundColor = "red";
    // Extra Codes Here ETC...
    var coordinates = getCaretCoordinates(Desired_ID, Desired_ID.selectionStart);
    var elementCoordinates = getElementCoords(Desired_ID);
    var topPosition = coordinates.top + elementCoordinates.top;
    var leftPosition = coordinates.left + elementCoordinates.left;
    alert(leftPosition + ", " + topPosition);
    // Extra Codes Here ETC...
}
</script>

所以我们的最后一次演示终于在https://jsfiddle.net/qjkkqdg2/2/