Textarea Helper plugin

Makes it possible to query the height of the textarea content and the XY coordinates of the caret position

jQuery TextRange

jQuery plugin for getting, setting, and replacing the selected text in input fields and textareas.

Rangy Inputs

jQuery plug-in for selection and caret manipulation within textareas and text inputs.

Caret

Manipulate the caret’s position in a text box or content-editable element.

jquery.selection

selection text/caret operation – jQuery pulgin | 選択範囲のテキスト操作 / キャレット操作