输入框光标定位实现

 

     /*
      *Cross browser routine for getting selected range/cursor position
      */
    function getElementSelection(that) {
        var position = {};
        if (that.selectionStart === undefined) {
            that.focus();
            var select = document.selection.createRange();
            position.length = select.text.length;
            select.moveStart('character', -that.value.length);
            position.end = select.text.length;
            position.start = position.end - position.length;
        } else {
            position.start = that.selectionStart;
            position.end = that.selectionEnd;
            position.length = position.end - position.start;
        }
        return position;
    }
    /**
     * Cross browser routine for setting selected range/cursor position
     */
    function setElementSelection(that, start, end) {
        if (that.selectionStart === undefined) {
            that.focus();
            var r = that.createTextRange();
            r.collapse(true);
            r.moveEnd('character', end);
            r.moveStart('character', start);
            r.select();
        } else {
            that.selectionStart = start;
            that.selectionEnd = end;
        }
    }