---
title: Expression
product: Form Library
description: Expression is a read-only question type that dynamically calculates values based on user input or predefined variables. This free demo for JavaScript shows how expressions can be used to estimate the total cost of a pizza order in real-time by multiplying the quantity by the price for each item on the menu and summing up these values.
framework: Angular
source: https://surveyjs.io/form-library/examples/expression-question-for-dynamic-form-calculations/angular
index: https://surveyjs.io/form-library/examples/overview.md
---

# Expression (Angular)

Expression is a read-only question type used to dynamically calculate values based on user input or predefined variables and display the calculated values in your form or survey. In this demo, expression questions calculate the cost of each pizza based on selected size and quantity and add up the costs to display the total of an order.

To create an Expression question, add an object to the [`elements`](https://surveyjs.io/form-library/documentation/api-reference/page-model#elements) array and specify the following properties within this object:

- `type`        
A question [type](https://surveyjs.io/form-library/documentation/api-reference/expression-model#getType). Set this property to `"expression"`.

- [`name`](https://surveyjs.io/form-library/documentation/api-reference/expression-model#name)        
A unique name that identifies the question.

- [`title`](https://surveyjs.io/form-library/documentation/api-reference/expression-model#title)       
A title for the question.

- [`expression`](https://surveyjs.io/form-library/documentation/api-reference/expression-model#expression)      
An expression used to calculate the value you want to display (see [Expressions](https://surveyjs.io/form-library/documentation/design-survey/conditional-logic#expressions)).

- *(Optional)* [`description`](https://surveyjs.io/form-library/documentation/api-reference/expression-model#description)       
Explanatory text displayed under the title.

Refer to the `json.js` file listing for more information.

## Files

### `src/app/components/json.ts`

```ts
export const json = {
  "elements": [
    {
      "type": "panel",
      "name": "neapolitan",
      "elements": [
        {
          "type": "expression",
          "name": "price_n",
          "minWidth": "220px",
          "title": "Pizza Neapolitan",
          "description": "tomato sauce, mozzarella, anchovies, bazil",
          "expression": "5 + {size_n}",
          "displayStyle": "currency"
        },
        {
          "type": "image",
          "name": "pic_n",
          "width": "180px",
          "minWidth": "180px",
          "maxWidth": "180px",
          "startWithNewLine": false,
          "imageLink": "https://api.surveyjs.io/private/Surveys/files?name=c5b0302a-d6c8-46b4-ac57-7d519d0df0d1",
          "contentMode": "image",
          "imageFit": "cover",
          "imageHeight": 80,
          "imageWidth": 180
        },
        {
          "type": "dropdown",
          "name": "size_n",
          "minWidth": "220px",
          "title": "Size",
          "titleLocation": "left",
          "defaultValue": 1,
          "choices": [
            { "value": 0, "text": "Small" },
            { "value": 1, "text": "Medium" },
            { "value": 2, "text": "Large" }
          ],
          "allowClear": false
        },
        {
          "type": "dropdown",
          "name": "qty_n",
          "minWidth": "220px",
          "startWithNewLine": false,
          "title": "Qty",
          "titleLocation": "left",
          "choices": [ 1, 2, 3, 4, 5 ]
        }
      ]
    },
    {
      "type": "panel",
      "name": "pepperoni",
      "elements": [
        {
          "type": "expression",
          "name": "price_p",
          "title": "Pepperoni",
          "description": "tomato sauce, pepperoni, red peppers, onion",
          "expression": "5 + {size_p}",
          "displayStyle": "currency"
        },
        {
          "type": "image",
          "name": "pic_p",
          "width": "180px",
          "minWidth": "180px",
          "maxWidth": "180px",
          "startWithNewLine": false,
          "imageLink": "https://api.surveyjs.io/private/Surveys/files?name=8bcd88b7-df19-466d-8622-19100e400383",
          "contentMode": "image",
          "imageFit": "cover",
          "imageHeight": 80,
          "imageWidth": 180
        },
        {
          "type": "dropdown",
          "name": "size_p",
          "minWidth": "220px",
          "title": "Size",
          "titleLocation": "left",
          "defaultValue": 1,
          "choicesFromQuestion": "size_n",
          "allowClear": false
        },
        {
          "type": "dropdown",
          "name": "qty_p",
          "minWidth": "220px",
          "startWithNewLine": false,
          "title": "Qty",
          "titleLocation": "left",
          "choicesFromQuestion": "qty_n"
        }
      ]
    },
    {
      "type": "panel",
      "name": "marinara",
      "elements": [
        {
          "type": "expression",
          "name": "price_m",
          "title": "Marinara",
          "description": "tomato sauce, tuna, shrimps, mushrooms, cheese, onion",
          "expression": "5 + {size_m}",
          "displayStyle": "currency"
        },
        {
          "type": "image",
          "name": "pic_m",
          "width": "180px",
          "minWidth": "180px",
          "maxWidth": "180px",
          "startWithNewLine": false,
          "imageLink": "https://api.surveyjs.io/private/Surveys/files?name=24735b69-0ffe-4e49-9c90-1d9db1c8b83b",
          "contentMode": "image",
          "imageFit": "cover",
          "imageHeight": 80,
          "imageWidth": 180
        },
        {
          "type": "dropdown",
          "name": "size_m",
          "minWidth": "220px",
          "title": "Size",
          "titleLocation": "left",
          "defaultValue": 1,
          "choicesFromQuestion": "size_n",
          "allowClear": false
        },
        {
          "type": "dropdown",
          "name": "qty_m",
          "minWidth": "220px",
          "startWithNewLine": false,
          "title": "Qty",
          "titleLocation": "left",
          "choicesFromQuestion": "qty_n"
        }
      ]
    },
    {
      "type": "expression",
      "name": "total",
      "title": "Total",
      "expression": "{price_n} * {qty_n} + {price_m} * {qty_m} + {price_p} * {qty_p}",
      "displayStyle": "currency"
    }
  ],
  "questionErrorLocation": "bottom"
};
```

### `src/app/components/survey.component.css`

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

### `src/app/components/survey.component.html`

```html
<survey [model]="model" style="position: absolute; top: 0; left: 0; right: 0; bottom: 0; height:100%"></survey>
```

### `src/app/components/survey.component.ts`

```ts
import { Component, OnInit } from "@angular/core";
import { Model } from "survey-core";
import { json } from "./json";
import "./survey.component.css";
import "survey-core/survey-core.min.css";

@Component({
    // tslint:disable-next-line:component-selector
    selector: "component-survey",
    templateUrl: "./survey.component.html",
    styleUrls: ["./survey.component.css"]
})
export class SurveyComponent implements OnInit {
    model: Model;
    ngOnInit() {
        const survey = new Model(json);
        survey.onComplete.add((sender, options) => {
            console.log(JSON.stringify(sender.data, null, 3));
        });
        this.model = survey;
    }
}
```

### `src/app/components/theme.ts`

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

### `src/app/app.component.css`

```css

```

### `src/app/app.component.html`

```html
<component-survey></component-survey>
```

### `src/app/app.component.ts`

```ts
import { Component } from "@angular/core";

@Component({
    selector: "app-root",
    templateUrl: "./app.component.html",
    styleUrls: ["./app.component.css"]
})
export class AppComponent {
    title = "CodeSandbox";
}
```

### `src/app/app.module.ts`

```ts
import { BrowserModule } from "@angular/platform-browser";
import { NgModule } from "@angular/core";

import { AppComponent } from "./app.component";
import { SurveyModule } from "survey-angular-ui";
import { SurveyComponent } from "./components/survey.component";

@NgModule({
    declarations: [AppComponent, SurveyComponent],
    imports: [BrowserModule, SurveyModule],
    providers: [],
    bootstrap: [AppComponent]
})
export class AppModule { }
```

### `src/environments/environment.prod.ts`

```ts
export const environment = {
    production: true
};
```

### `src/environments/environment.ts`

```ts
// The file contents for the current environment will overwrite these during build.
// The build system defaults to the dev environment which uses `environment.ts`, but if you do
// `ng build --env=prod` then `environment.prod.ts` will be used instead.
// The list of which env maps to which file can be found in `.angular-cli.json`.

export const environment = {
    production: false
};
```

### `src/index.html`

```html
<app-root></app-root>
```

### `src/main.ts`

```ts
import { enableProdMode } from "@angular/core";
import { platformBrowserDynamic } from "@angular/platform-browser-dynamic";

import { AppModule } from "./app/app.module";
import { environment } from "./environments/environment";

if (environment.production) {
    enableProdMode();
}

platformBrowserDynamic()
    .bootstrapModule(AppModule)
    .catch(err => console.log(err));
```

### `src/polyfills.ts`

```ts
/**
 * This file includes polyfills needed by Angular and is loaded before the app.
 * You can add your own extra polyfills to this file.
 *
 * This file is divided into 2 sections:
 *   1. Browser polyfills. These are applied before loading ZoneJS and are sorted by browsers.
 *   2. Application imports. Files imported after ZoneJS that should be loaded before your main
 *      file.
 *
 * The current setup is for so-called "evergreen" browsers; the last versions of browsers that
 * automatically update themselves. This includes Safari >= 10, Chrome >= 55 (including Opera),
 * Edge >= 13 on the desktop, and iOS 10 and Chrome on mobile.
 *
 * Learn more in https://angular.io/docs/ts/latest/guide/browser-support.html
 */

/***************************************************************************************************
 * BROWSER POLYFILLS
 */

/** IE9, IE10 and IE11 requires all of the following polyfills. **/
// import 'core-js/es6/symbol';
// import 'core-js/es6/object';
// import 'core-js/es6/function';
// import 'core-js/es6/parse-int';
// import 'core-js/es6/parse-float';
// import 'core-js/es6/number';
// import 'core-js/es6/math';
// import 'core-js/es6/string';
// import 'core-js/es6/date';
// import 'core-js/es6/array';
// import 'core-js/es6/regexp';
// import 'core-js/es6/map';
// import 'core-js/es6/weak-map';
// import 'core-js/es6/set';

/** IE10 and IE11 requires the following for NgClass support on SVG elements */
// import 'classlist.js';  // Run `npm install classlist.js`.

/** IE10 and IE11 requires the following for the Reflect API. */
// import 'core-js/es6/reflect';

/** Evergreen browsers require these. **/
// Used for reflect-metadata in JIT. If you use AOT (and only Angular decorators), you can remove.
import "core-js/proposals/reflect-metadata";

/**
 * Required to support Web Animations `@angular/platform-browser/animations`.
 * Needed for: All but Chrome, Firefox and Opera. http://caniuse.com/#feat=web-animation
 **/
// import 'web-animations-js';  // Run `npm install web-animations-js`.

/***************************************************************************************************
 * Zone JS is required by default for Angular itself.
 */
import "zone.js/dist/zone"; // Included with Angular CLI.

/***************************************************************************************************
 * APPLICATION IMPORTS
 */
```

### `src/styles.css`

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

### `src/typings.d.ts`

```ts
/* SystemJS module definition */
declare var module: NodeModule;
interface NodeModule {
    id: string;
}
```

### `.angular-cli.json`

```json
{
  "apps": [
    {
      "root": "src",
      "outDir": "dist",
      "assets": [ "assets", "favicon.ico" ],
      "index": "index.html",
      "main": "main.ts",
      "polyfills": "polyfills.ts",
      "prefix": "app",
      "styles": [ "styles.css" ],
      "scripts": [ ],
      "environmentSource": "environments/environment.ts",
      "environments": {
        "dev": "environments/environment.ts",
        "prod": "environments/environment.prod.ts"
      }
    }
  ]
}
```

### `_tsconfig.json`

```json
{
  "compileOnSave": false,
  "compilerOptions": {
    "baseUrl": "./",
    "outDir": "./dist/out-tsc",
    "sourceMap": true,
    "declaration": false,
    "allowSyntheticDefaultImports": true,
    "downlevelIteration": true,
    "experimentalDecorators": true,
    "moduleResolution": "node",
    "importHelpers": true,
    "resolveJsonModule": true,
    "target": "es2015",
    "module": "es2020",
    "lib": [
      "es2018",
      "dom"
    ]
  }
}
```

### `package.json`

```json
{
  "name": "surveyjs-angular",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build --prod",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "14.1.1",
    "@angular/cdk": "14.1.1",
    "@angular/common": "14.1.1",
    "@angular/compiler": "14.1.1",
    "@angular/core": "14.1.1",
    "@angular/forms": "14.1.1",
    "@angular/platform-browser": "14.1.1",
    "@angular/platform-browser-dynamic": "14.1.1",
    "@angular/router": "14.1.1",
    "core-js": "3.6.4",
    "rxjs": "6.5.4",
    "survey-core": "latest",
    "survey-angular-ui": "latest",
    "tslib": "1.13.0",
    "zone.js": "0.11.7"
  },
  "devDependencies": {
    "@angular/cli": "1.6.6",
    "@angular/compiler-cli": "^5.2.0",
    "@angular/language-service": "^5.2.0",
    "@types/core-js": "0.9.46",
    "@types/jasmine": "~2.8.3",
    "@types/jasminewd2": "~2.0.2",
    "@types/node": "~6.0.60",
    "codelyzer": "^4.0.1",
    "jasmine-core": "~2.8.0",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~2.0.0",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "^1.2.1",
    "karma-jasmine": "~1.1.0",
    "karma-jasmine-html-reporter": "^0.2.2",
    "protractor": "~5.1.2",
    "ts-node": "~4.1.0",
    "tslint": "~5.9.1",
    "typescript": "3.9.7"
  },
  "keywords": [ "angular", "surveyjs" ],
  "description": "SurveyJS-Angular example project"
}
```

## Other Frameworks

- [React](https://surveyjs.io/form-library/examples/expression-question-for-dynamic-form-calculations/reactjs.md)
- [Vue 3](https://surveyjs.io/form-library/examples/expression-question-for-dynamic-form-calculations/vue3js.md)
- [jQuery](https://surveyjs.io/form-library/examples/expression-question-for-dynamic-form-calculations/jquery.md)
- [Vanilla JS](https://surveyjs.io/form-library/examples/expression-question-for-dynamic-form-calculations/vanillajs.md)