---
title: Delayed File Upload
product: Form Library
description: Learn how to effectively implement delayed file upload methods to optimize storage space and enhance user experience. Follow the step-by-step instructions for JavaScript to handle file uploads, downloads, and storage within various event handlers.
framework: Vue 3
source: https://surveyjs.io/form-library/examples/delayed-file-upload/vue3js
index: https://surveyjs.io/form-library/examples/overview.md
---

# Delayed File Upload (Vue 3)

Delayed file upload is a technique that enables you to postpone file upload until a certain moment. This technique helps save storage space on your server: if a user selects a file and then changes it to another, the first file won't be uploaded. This demo shows how to upload files when a survey is completed. Until that moment, files are stored in a variable as base64-encoded strings.

To implement delayed file upload, program different functionalities within the following event handlers:

- [`onUploadFiles`](https://surveyjs.io/form-library/documentation/api-reference/survey-data-model#onUploadFiles)\
Add files to a variable that acts as a temporary file storage and load file previews.

- [`onClearFiles`](https://surveyjs.io/form-library/documentation/api-reference/survey-data-model#onClearFiles)\
Remove all or individual files from the temporary file storage.

- [`onComplete`](https://surveyjs.io/form-library/documentation/api-reference/survey-data-model#onComplete)\
Upload files to a server and save metadata about them as the question value.

For more information, view code listings for Angular, React, Vue, jQuery, or Vanilla JavaScript.

> In this demo, files are uploaded to SurveyJS servers from where they are then deleted after a predefined period of time. We strongly encourage you to use your own servers for file uploads when you use SurveyJS to collect sensitive respondent data in your application.

## 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">


function displaySurveyResults(result, data) {
    const text = JSON.stringify(data || result.data, null, 3);
    ["content-result-json-code", "surveyResult"].forEach(id => {
        const el = document.getElementById(id);
        if (el) el.textContent = text;
    });
}
</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 "./index.css";
    import { json } from "./json";

    const survey = new Model(json);
    survey.onComplete.add((sender, options) => {
        console.log(JSON.stringify(sender.data, null, 3));
    });
    const tempFileStorage = {}; // Temporary storage for uploaded files
    
    function getStorageKey({ name, parent }) {
        let storageKey = name;
        // Check if the file upload is inside a dynamic panel and adjust the storage key accordingly
        if (parent && parent.parentQuestion && parent.parentQuestion.getType() === "paneldynamic") {
            const dynPanel = parent.parentQuestion;
            const panel = parent;
            const i = dynPanel.visiblePanels.indexOf(panel);
            storageKey = dynPanel.name + "_" + i + "_" + name;
        }
        return storageKey;
    }
    
    function getQuestionByStorageKey(survey, storageKey) {
        let q = survey.getQuestionByName(storageKey);
        if (!q) {
            // Parse storageKey to determine if it belongs to a dynamic panel
            const keyParts = storageKey.split("_");
            const dynPanelName = keyParts[0];
    
            const dynPanel = survey.getQuestionByName(dynPanelName);
            if (dynPanel && dynPanel.getType() === "paneldynamic") {
                const i = parseInt(keyParts[1], 10);
                const qName = keyParts.slice(2).join("_"); // Handle cases when the question name contains underscores
                q = dynPanel.panels[i] && dynPanel.panels[i].getQuestionByName(qName);
            }
        }
        return q;
    }
    
    survey.onUploadFiles.add((_, options) => {
        const key = getStorageKey(options.question);
        // Store files in a temporary storage
        if (tempFileStorage[key] !== undefined) {
            tempFileStorage[key] = tempFileStorage[key].concat(options.files);
        } else {
            tempFileStorage[key] = options.files;
        }
    
        // Generate file previews
        const content = [];
        options.files.forEach((file) => {
            const fileReader = new FileReader();
            fileReader.onload = () => {
                content.push({
                    name: file.name,
                    type: file.type,
                    content: fileReader.result,
                    file: file,
                });
                if (content.length === options.files.length) {
                    // Return a file preview
                    options.callback(
                        content.map((fileContent) => ({
                            file: fileContent.file,
                            content: fileContent.content,
                        }))
                    );
                }
            };
            fileReader.readAsDataURL(file);
        });
    });
    
    // Handles file removal
    survey.onClearFiles.add((_, options) => {
        const key = getStorageKey(options.question);
    
        // Clear all files if "Clear All" is clicked
        if (options.fileName === null) {
            tempFileStorage[key] = [];
            options.callback("success");
            return;
        }
    
        // Remove a specific file
        const tempFiles = tempFileStorage[key];
        if (tempFiles && tempFiles.length > 0) {
            const fileInfoToRemove = tempFiles.find(
                (file) => file.name === options.fileName
            );
            if (fileInfoToRemove) {
                const index = tempFiles.indexOf(fileInfoToRemove);
                tempFiles.splice(index, 1);
            }
        }
        options.callback("success");
    });
    
    // Handles file uploads when the survey is completed
    survey.onComplete.add((result) => {
        displaySurveyResults(result, { data: "Please wait for files to upload." });
        const storageKeys = Object.keys(tempFileStorage);
    
        if (storageKeys.length === 0) {
            displaySurveyResults(result);
            return;
        }
        // Process each stored file set for upload
        const uploadPromises = storageKeys.map((key) => {
            const filesToUpload = tempFileStorage[key];
            const formData = new FormData();
            filesToUpload.forEach((file) => {
                formData.append(file.name, file);
            });
    
            return fetch("https://api.surveyjs.io/private/Surveys/uploadTempFiles", {
                method: "POST",
                body: formData,
            })
                .then((response) => response.json())
                .then((data) => {
                    // Assign the uploaded file metadata to the corresponding question
                    const q = getQuestionByStorageKey(survey, key);
                    if (q) {
                        q.value = filesToUpload.map((file) => ({
                            file: file,
                            type: file.type,
                            content: "https://api.surveyjs.io/private/Surveys/getTempFile?name=" + data[file.name]
                        }));
                    }
                })
                .catch((error) => {
                    console.error("Error:", error);
                });
        });
    
        // Wait for all uploads to complete before displaying survey results
        Promise.all(uploadPromises).then(() => {
            displaySurveyResults(result);
        });
    });
</script>
```

### `src/index.css`

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

### `src/json.ts`

```ts
export const json = {
  "elements": [
    {
      "type": "file",
      "title": "Please upload your files",
      "name": "files",
      "storeDataAsText": false,
      "allowMultiple": true,
      "maxSize": 102400
    }
  ]
};
```

### `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/delayed-file-upload/angular.md)
- [React](https://surveyjs.io/form-library/examples/delayed-file-upload/reactjs.md)
- [jQuery](https://surveyjs.io/form-library/examples/delayed-file-upload/jquery.md)
- [Vanilla JS](https://surveyjs.io/form-library/examples/delayed-file-upload/vanillajs.md)