---
title: Dynamic Default Question Values
product: Form Library
description: Learn how to preconfigure question values using values of other questions, date and math functions, or custom functions defined in your JavaScript code. View a free demo for JavaScript to learn more.
framework: React
source: https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/reactjs
index: https://surveyjs.io/form-library/examples/overview.md
---

# Dynamic Default Question Values (React)

SurveyJS Form Library allows you to specify default question values. Questions use them until proper values are specified by a user or programmatically. If the proper values are never specified, default values are saved in survey results.

You can specify static default values or calculate default values dynamically. To specify a static default question value, assign it to the question's [`defaultValue`](https://surveyjs.io/form-library/documentation/api-reference/question#defaultValue) property.

To calculate a default question value dynamically, assign a logical expression to the question's [`defaultValueExpression`](https://surveyjs.io/form-library/documentation/api-reference/question#defaultValueExpression) property as shown in this demo. This expression will be evaluated for the first time when the survey begins, and then re-evaluated again each time any question value changes. Your expression can include the following dynamic elements:

- [Question values](https://surveyjs.io/form-library/documentation/design-survey/conditional-logic#question-values)
- [Variables](https://surveyjs.io/form-library/documentation/design-survey/conditional-logic#variables)
- [Calculated values](https://surveyjs.io/form-library/documentation/design-survey/conditional-logic#calculated-values)
- [Built-in functions](https://surveyjs.io/form-library/documentation/design-survey/conditional-logic#built-in-functions)
- [Custom JavaScript functions](https://surveyjs.io/form-library/documentation/design-survey/conditional-logic#custom-functions)

Follow the links above for information on how to use these elements to specify dynamic default question values.

## Files

### `public/index.html`

```html
<div id="surveyElement" style="position: absolute; top: 0; left: 0; right: 0; bottom: 0; min-height: 100%; height:100%"></div>
```

### `src/SurveyComponent.jsx`

```js
import React from "react";
import { Model } from "survey-core";
import { Survey } from "survey-react-ui";
import "survey-core/survey-core.min.css";
import "./index.css";
import { json } from "./json";
import { registerFunction } from "survey-core";

// Register a custom expression function
function calculateCircleArea(params) {
    let radius = params[0];
    let area = Math.PI * Math.pow(radius, 2);
    return area;
}
registerFunction({ name: "calculateCircleArea", func: calculateCircleArea });
function SurveyComponent() {
    const survey = new Model(json);
    survey.onComplete.add((sender, options) => {
        console.log(JSON.stringify(sender.data, null, 3));
    });
    survey.setVariable('userName', 'Jane Doe');
    
    return (<Survey model={survey} />);
}

export default SurveyComponent;
```

### `src/index.css`

```css
/* You can add your custom CSS here. */
```

### `src/index.js`

```js
import React from "react";
import { createRoot } from "react-dom/client";
import SurveyComponent from "./SurveyComponent";

const root = createRoot(document.getElementById("surveyElement"));
root.render(<SurveyComponent />);
```

### `src/json.js`

```js
export const json = {
  "pages": [
    {
      "name": "page1",
      "elements": [
        {
          "type": "text",
          "title": "Survey Variables in Expressions",
          "description": "Concatenate a string literal with a survey variable to define a default value.",
          "name": "user-name",
          "defaultValueExpression": "'Hello, ' + {userName}"
        },
        {
          "type": "panel",
          "name": "car-info",
          "elements": [
            {
              "type": "dropdown",
              "name": "car-brand",
              "title": "Which is the brand of your car?",
              "choices": [
                "Ford",
                "Vauxhall",
                "Volkswagen",
                "Nissan",
                "Audi",
                "Mercedes-Benz",
                "BMW",
                "Peugeot",
                "Toyota",
                "Citroen"
              ],
              "defaultValue": "Audi",
              "showOtherItem": true,
              "showNoneItem": true
            },
            {
              "type": "text",
              "name": "your-car",
              "startWithNewLine": false,
              "title": "Your Car",
              "defaultValueExpression": "{car-brand}"
            }
          ],
          "title": "Question Values in Expressions",
          "description": "Use a value from a drop-down menu as a default value for a text box."
        },
        {
          "type": "paneldynamic",
          "name": "vacation-info",
          "title": "Default Value Expressions in Dynamic Panels",
          "panelCount": 1,
          "description": "Use `{panel.questionName}` to reference a nested question's value in expressions.",
          "templateElements": [
            {
              "type": "dropdown",
              "name": "country",
              "title": "Select a country",
              "defaultValue": "Cyprus",
              "choicesByUrl": {
                "url": "https://surveyjs.io/api/CountriesExample",
                "valueName": "name"
              }
            },
            {
              "type": "text",
              "name": "start-date",
              "title": "Select a vacation start date",
              "description": "Use the `today()` function to specify the current date.",
              "defaultValueExpression": "today()",
              "inputType": "date"
            },
            {
              "type": "text",
              "name": "end-date",
              "startWithNewLine": false,
              "title": "Select a vacation end date",
              "description": "Use the `today(daysToAdd)` function to shift the current date to a specified number of days.",
              "defaultValueExpression": "today(10)",
              "validators": [
                {
                  "type": "expression",
                  "text": "End date should be greater than start date",
                  "expression": "{panel.end-date} empty or {panel.end-date} > {panel.start-date}"
                }
              ],
              "inputType": "date"
            },
            {
              "type": "text",
              "name": "days-spent",
              "title": "Days spent in {panel.country}",
              "titleLocation": "left",
              "defaultValueExpression": "iif({panel.start-date} < {panel.end-date}, diffDays({panel.start-date}, {panel.end-date}))"
            }
          ]
        },
        {
          "type": "matrixdropdown",
          "name": "company-role",
          "title": "Default Value Expressions in Matrix Cells",
          "description": "Use `{row.questionName}` to reference a question from the same row in expressions. In this matrix, select \"No\" in the first column, and the second column row cell will also be set to \"No\".",
          "columns": [
            {
              "name": "employee-role-availability",
              "title": "Do you have the following employee role in your company?"
            },
            {
              "name": "isStaffed",
              "title": "Is this position currently filled?",
              "defaultValueExpression": "iif({row.employee-role-availability} = 'No', 'No', '')"
            }
          ],
          "choices": [
            "Yes",
            "No"
          ],
          "rows": [
            "Sales Representative",
            "Software Developer",
            "Human Resources Manager"
          ]
        },
        {
          "type": "panel",
          "name": "math-calculations",
          "elements": [
            {
              "type": "text",
              "name": "radius",
              "title": "Enter circle radius",
              "defaultValue": 3,
              "inputType": "numeric",
              "min": 0,
              "max": 10
            },
            {
              "type": "text",
              "title": "Area of the circle",
              "name": "circle-area",
              "defaultValueExpression": "calculateCircleArea({radius})",
              "startWithNewLine": false
            }
          ],
          "title": "Custom JavaScript Function",
          "description": "Register a custom JavaScript function to perform custom calculations."
        }
      ]
    }
  ],
  "questionErrorLocation": "bottom"
};
```

### `src/theme.js`

```js
export const themeJson = {};
```

### `package.json`

```json
{
  "dependencies": {
    "react": "latest",
    "react-dom": "latest",
    "survey-core": "latest",
    "survey-react-ui": "latest"
  },
  "devDependencies": {
    "react-scripts": "latest"
  }
}
```

## Other Frameworks

- [Angular](https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/angular.md)
- [Vue 3](https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/vue3js.md)
- [jQuery](https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/jquery.md)
- [Vanilla JS](https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/vanillajs.md)