Predefine Answers

You can set a question's defaultValue, which will be used until a proper value is specified by a user or programmatically. If the proper value is never specified, defaultValue is saved in the survey results.

const surveyJson = {
  "elements": [{
    "name": "subscribed",
    "type": "checkbox",
    "title": "I agree to receive weekly newsletters"
    "defaultValue": true
  }]
}

You can set the question value property or call the Survey's setValue(questionName, newValue) method to change the value at any point in your application:

import { Model } from "survey-core";

const survey = new Model(surveyJson);
survey.setValue("subscribed", false);