How to select a scroll text box from a row to a row

// ======================================
// Function: accurately locates the scroll text box
// Input parameters:
// Self scroll text box object
// _ Startline start line
// _ Endline end row
// _ Start position of the Start row of startpoint
// _ Endpoint end position of the number of end rows
// Call method:
// ① The same row, from the starting position to the ending position:
// Seltolinepoint (self, 2, 2, 0/1, 0)
// ② Different rows, from a starting position to the ending position:
// Seltolinepoint (self, 2, 4, 3, 0)
// ③ Different rows, from a starting position to a ending position:
// Seltolinepoint (self, 2, 4, 3, 9)
// ======================================
Function seltolinepoint (self, _ Startline, _ endline, _ startpoint, _ endpoint, _ Len ){
VaR src = self;
VaR OTR = self. createTextRange ();
VaR text = self. innertext;
VaR textlength = text. length;
 
Conts = [0];
Startx = SRC. createTextRange (). getclientrects () [0]. Left;
Starty = SRC. createTextRange (). getclientrects () [0]. Top;
Stepy = 3; // the step that the cursor moves down. It cannot be greater than the word height in textarea.
Currentscr = 0; // current scroll bar position
Stepscr = 30; // the step of scroll down, which cannot be greater than the height of textarea
 
While (1 ){
SRC. scrolltop = currentscr
Currenty = starty
While (1) {// The cursor moves down from the beginning of the textarea content, traversing each row, and recording the positions of each row in the conts []
OTR. movetopoint (startx, currenty)
OTR. moveend ("character", textlength)
VaR _ otr_line_length = OTR. Text. length;
Cont = textlength-_ otr_line_length;
If (cont> = textlength ){
Break
}
If (cont> conts [conts. Length-1]) {
Conts [conts. Length] = cont
}
Currenty + = stepy
}
If (currentscr> = SRC. scrollheight ){
Break
}
Currentscr + = stepscr;
}
 
If (_ endline = "")
_ Endline = _ Startline;
_ Startline = parseint (_ Startline );
_ Endline = parseint (_ endline );
 
If (isfinite (_ Startline) & isfinite (_ endline) & _ Startline> 0 & _ endline> 0 ){
// Check the parameter Validity
If (_ Startline> conts. Length | _ endline> conts. Length ){
Alert ("only" + conts. Length + "rows in total, check and try again. ");
Return;
}

// If the end row is forcibly adjusted before the start row
If (_ endline <_ Startline ){
_ Endline = _ Startline;
End. value = _ endline;
}

SRC. scrolltop = 0;
OTR. movetopoint (startx, starty); // The cursor returns to the beginning of the textarea content
St = conts [_ Startline-1];

If (ST> _ startpoint ){
St = ST + _ startpoint;
} Else {
VaR _ righttextlen = 0;
For (VAR m = 0; m <conts. length; m ++ ){
If (conts [m] <_ startpoint ){
_ Righttextlen = _ startpoint-conts [m];
St = _ startpoint-_ righttextlen;
If (_ endline = _ Startline ){
_ Endline ++;
}
} Else {
Break;
}
}

If (ST + _ righttextlen <textlength ){
St = ST + _ righttextlen;
}

}

Texprestart = text. substr (0, St );
Texprestart = text. substr (0, ST ). replace (/R/g, ""); // The string from the beginning of the textarea content to the start point. Since the movestart method treats rn as a character, you need to modify the count.

St = texprestart. length;
OTR. movestart ("character", St );
En = textlength;
If (_ endline <conts. Length ){
En = conts [_ endline];
If (_ endpoint> 0 ){
VaR lalinelen = conts [_ endline]-conts [_ endline-1];
En = en-lalinelen + _ endpoint;
}
}
Texpreend = text. substr (0, en ). replace (/R/g, "") // The string from the beginning of the textarea content to the end point. Because the moveend method treats rn as a character, the Count needs to be corrected.
En = texpreend. Length
VaR _ endx = en-ST;
OTR. moveend ("character", _ endx );
OTR. Select ();
}
 
}