deduceComposition = function (text) {
                var oldState = _this._textAreaState;
                var newState = textAreaState_1.TextAreaState.selectedText(text);
                var typeInput = {
                    text: newState.value,
                    replaceCharCnt: oldState.selectionEnd - oldState.selectionStart
                };
                return [newState, typeInput];
            }
Deduce the composition input from a string.