Example of cursor position tool function implemented by js

<p>Text box：</p>
<textarea name=""  cols="30" rows="10">
sASASADASDasfaDFDsfsDFAfdFADf
</textarea>
<button type="button" >Select a specific range of text</button>
<button type="button" >Insert text after cursor</button>
<br>
<hr>
<br>
<input type="number" name="" >
<button type="button" >Set cursor position</button>
<br>
<hr>
<br>
<p >I'm a text that can be selected，Please open the console to view。I'm a text that can be selected，Please open the console to view。I'm a text that can be selected，Please open the console to view。</p>

/**
 * Cursor position component
 * ## method of selectRange object:
 * (1)(ele) [Create a new object obtained by cursor position]
       parameter:
         ele {{JavaScript DOM}} The element where the cursor is located, native JavaScript DOM
 * (2)() [Get the current coordinate position]
 * (3)(pos) [Set the current cursor position]
       parameter:
         pos {{Int}} Current cursor position
 * (4)() [Get selected text]
 * (5)(startPos, endPos) [Select text with a specific range (only textarea and input)]
 * Parameters:
         startPos {{Int}} Start Pos
         endPos {{Int}} End Position
 * (6)(value) [Insert text after cursor]
 * Parameters:
         value {{String}} Text to be inserted
 *
 *
 * ## Examples:
 * (EleDom).getCurPos(); // Get the current coordinate position
 * (EleDom).setCurPos(pos); // Set the current cursor position to pos
 * (EleDom).getSelectText(); // Get selected text
 * (EleDom).setSelectText(startPos, endPos); // Select text from the range startPos to endPos
 * (EleDom).insertAfterText(value); // Insert text with value after the cursor
 */
var selectRange = function(ele){
  this.__element = ele;
};
// Create a new object to obtain the cursor position = function(ele){
  if(ele) {
    return new selectRange(ele);
  } else {
    return {};
  }
};
 = {
  constructor:selectRange,
  // Get the current coordinate position  getCurPos: function() {
    var _this = this,
      textDom = _this.__element;
    // Get the cursor position    var cursorPos = 0;
    if () {
      // IE Support
      ();
      var selectRange = ();
       ('character', -);
      cursorPos = ;
    }else if ( ||  == '0') {
      // Firefox support
      cursorPos = ;
    }
    return cursorPos;
  },
  /**
   * Set the current cursor position
   * Parameters:
   * pos [Int] Current cursor position
   */
  setCurPos: function(pos) {
    var _this = this,
      textDom = _this.__element;
    if() {
      // IE Support
      ();
      (pos, pos);
    }else if () {
      // Firefox support
      var range = ();
      (true);
      ('character', pos);
      ('character', pos);
      ();
    }
  },
  // Get selected text  getSelectText: function() {
    var _this = this,
      textDom = _this.__element,
      userSelection,
      text = "";
    if () {
      // Firefox support
      userSelection = ();
    } else if () {
      // IE Support
      userSelection = ();
    }
    if (!(text = )) {
      text = userSelection;
    }
    return text;
  },
  /**
   * Select text with a specific range (only textarea and input)
   * Parameters:
   * startPos [Int] Start Pos
   * endPos [Int] End Position
   */
  setSelectText: function(startPos, endPos) {
    var _this = this,
      textDom = _this.__element,
      startPos = parseInt(startPos),
      endPos = parseInt(endPos),
      textLength = ;
    if(textLength){
      if(!startPos){
        startPos = 0;
      }
      if(!endPos){
        endPos = textLength;
      }
      if(startPos > textLength){
        startPos = textLength;
      }
      if(endPos > textLength){
        endPos = textLength;
      }
      if(startPos < 0){
        startPos = textLength + startPos;
      }
      if(endPos < 0){
        endPos = textLength + endPos;
      }
      if(){
        // IE Support
        var range = ();
        ("character",-textLength);
        ("character",-textLength);
        ("character", startPos);
        ("character",endPos);
        ();
      }else{
        // Firefox support
        (startPos, endPos);
        ();
      }
    }
  },
  /**
   * Insert text after cursor
   * Parameters:
   * value [String] Text to be inserted
   */
  insertAfterText: function(value) {
    var _this = this,
      textDom = _this.__element,
      selectRange;
    if () {
      // IE Support
      ();
      selectRange = ();
       = value;
      ();
    }else if ( ||  == '0') {
      // Firefox support
      var startPos = ;
      var endPos = ;
      var scrollTop = ;
       = (0, startPos) + value + (endPos, );
      ();
       = startPos + ;
       = startPos + ;
       = scrollTop;
    }
    else {
       += value;
      ();
    }
  }
};
// ===============================================
// Instance codevar textareaDom = ("#textarea"),
  setCurPosInput = ("#input"),
  setCurPosBtn = ("#setCurPosBtn"),
  selectText = ("#selectText"),
  setSelectTextBtn = ("#setSelectText"),
  insertAfterTextBtn = ("#insertAfterText");
// Get the current cursor position("keydown", function() {
  ("getCurPos: " + (textareaDom).getCurPos());
}, false);
// Set the current cursor position("click", function() {
  var curPos = parseInt();
  ("curPos: " + curPos);
  (textareaDom).setCurPos(curPos);
}, false);
// Get selected text("mouseup", function() {
  ("selectText: " + (this).getSelectText());
});
// Select text in a specific range("click", function() {
  (textareaDom).setSelectText(0, 21);
}, false);
// Insert text after cursor("click", function() {
  var insertText = "===hello world, I'm insert content.===";
  (textareaDom).insertAfterText(insertText);
}, false);