Using a checkbox with react throws a warning about an uncontrolled input becoming controlled

[jdalegonzalez]

This issue is in SurveyQuestionCheckboxItem::render. The code:

var isChecked = this.question.value && this.question.value.indexOf(this.item.value) > -1;

sets isChecked to undefined, which means that the input created by SuveryQuestionCheckboxItem::renderCheckbox sets the checked attribute of the input item it creates to undefined. Having an undefined value for a checked attribute makes react decide that the item is uncontrolled. A later call to setState in SuveryQuestionCheckboxItem::handleOnChange makes react believe the input should be controlled and causes the warning to get thrown.

var isChecked = t(his.question.value && this.question.value.indexOf(this.item.value) > -1)||false;

prevents the warning - I'll issue a pull request for this change.

HOWEVER: I'm not enough of a react guru to know if the value for the checkbox is being handled correctly from a react perspective or not.