---
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: Vue 3
source: https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/vue3js
index: https://surveyjs.io/form-library/examples/overview.md
---

# Dynamic Default Question Values (Vue 3)

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="app" style="position: absolute; top: 0; left: 0; right: 0; bottom: 0; height:100%"></div>
```

### `src/App.vue`

```html
<script lang="ts">
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 });
</script>
<template>
    <SurveyComponent :model="survey" />
</template>
<script setup lang="ts">
    import { Model } from "survey-core";
    import { SurveyComponent } from "survey-vue3-ui";
    import "survey-core/survey-core.min.css";
    import { registerFunction } from "survey-core";
    import "./index.css";
    import { json } from "./json";

    const survey = new Model(json);
    survey.onComplete.add((sender, options) => {
        console.log(JSON.stringify(sender.data, null, 3));
    });
    survey.setVariable('userName', 'Jane Doe');
    
</script>
```

### `src/index.css`

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

### `src/json.ts`

```ts
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/main.ts`

```ts
import { createApp } from "vue";
import App from "./App.vue";

const app = createApp(App);
app.mount("#app");
```

### `src/shims-vue.d.ts`

```ts
/* eslint-disable */
declare module "*.vue" {
    import type { DefineComponent } from "vue"
    const component: DefineComponent<{}, {}, any>
    export default component
}
```

### `src/theme.ts`

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

### `.eslintrc.js`

```js
module.exports = {
    root: true,
    env: {
        node: true
    },
    extends: [
        "plugin:vue/vue3-essential",
        "eslint:recommended",
        "@vue/typescript/recommended",
        "@vue/prettier",
        "@vue/prettier/@typescript-eslint"
    ],
    parserOptions: {
        ecmaVersion: 2020
    },
    rules: {
        "no-console": process.env.NODE_ENV === "production" ? "warn" : "off",
        "no-debugger": process.env.NODE_ENV === "production" ? "warn" : "off"
    },
    overrides: [
        {
            files: [
                "**/__tests__/*.{j,t}s?(x)",
                "**/tests/unit/**/*.spec.{j,t}s?(x)"
            ],
            env: {
                jest: true
            }
        }
    ]
};
```

### `babel.config.js`

```js
module.exports = {
  presets: ["@vue/cli-plugin-babel/preset"]
};
```

### `package.json`

```json
{
  "name": "surveyjs-library-vue3",
  "version": "0.1.0",
  "scripts": {
    "serve": "vue-cli-service serve",
    "build": "vue-cli-service build",
    "lint": "vue-cli-service lint"
  },
  "dependencies": {
    "core-js": "^3.6.5",
    "tslib": "2.6.1",
    "vue": "^3.4.1",
    "survey-core": "latest",
    "survey-vue3-ui": "latest",
    "vue-router": "^4.0.0-0",
    "vuex": "^4.0.0-0"
  },
  "devDependencies": {
    "@typescript-eslint/eslint-plugin": "^2.33.0",
    "@typescript-eslint/parser": "^2.33.0",
    "@vue/cli-plugin-babel": "~4.5.0",
    "@vue/cli-plugin-eslint": "~4.5.0",
    "@vue/cli-plugin-pwa": "~4.5.0",
    "@vue/cli-plugin-router": "~4.5.0",
    "@vue/cli-plugin-typescript": "~4.5.0",
    "@vue/cli-plugin-vuex": "~4.5.0",
    "@vue/cli-service": "~4.5.0",
    "@vue/compiler-sfc": "^3.0.0",
    "@vue/eslint-config-prettier": "^6.0.0",
    "@vue/eslint-config-typescript": "^5.0.2",
    "@vue/test-utils": "^2.0.0-0",
    "eslint": "^6.7.2",
    "eslint-plugin-prettier": "^3.1.3",
    "eslint-plugin-vue": "^7.0.0-0",
    "node-sass": "^4.12.0",
    "prettier": "^1.19.1",
    "sass-loader": "^8.0.2",
    "typescript": "~3.9.3"
  }
}
```

### `tsconfig.json`

```json
{
  "compilerOptions": {
    "target": "esnext",
    "module": "esnext",
    "strict": true,
    "jsx": "preserve",
    "importHelpers": true,
    "moduleResolution": "node",
    "skipLibCheck": true,
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "sourceMap": true,
    "baseUrl": ".",
    "types": [
      "webpack-env",
      "jest"
    ],
    "paths": {
      "@/*": [
        "src/*"
      ]
    },
    "lib": [
      "esnext",
      "dom",
      "dom.iterable",
      "scripthost"
    ]
  },
  "include": [
    "src/**/*.ts",
    "src/**/*.tsx",
    "src/**/*.vue",
    "tests/**/*.ts",
    "tests/**/*.tsx"
  ],
  "exclude": [
    "node_modules"
  ]
}
```

## Other Frameworks

- [Angular](https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/angular.md)
- [React](https://surveyjs.io/form-library/examples/specify-default-question-value-dynamically/reactjs.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)