Number Lines

script

// Number the selected lines (or all lines) with colon and
// two spaces after each line number.

// Define the text that's going to be numbered.
let st, len;
if (editor.getSelectedRange()[1] > 0) { // use selected lines
	[st, len] = editor.getSelectedLineRange();
}
else { // use full text
	[st, len] = [0, editor.getText().length];
}
let lnText = editor.getTextInRange(st, len);
if (lnText.endsWith("\n")) { // trailing LF doesn't count
	lnText = lnText.slice(0, -1);
	len -= 1;
}

// Break the text into lines and number them.
// Right-justify the numbers and put a colon and
// two spaces after the line number.
var lines = lnText.split('\n');
var numLines = lines.length;
var width = Math.floor(Math.log(numLines)*Math.LOG10E) + 1;
var numbered = [];
var lNum;
for (var i=0; i<numLines; i++) {
  lNum = i + 1;
  numbered.push(lNum.toString().padStart(width) + ':  ' + lines[i]);
}

// Replace the original text with the line-numbered text.
let rep = numbered.join('\n')
editor.setTextInRange(st, len, rep);
editor.setSelectedRange(st, rep.length);