Angular
How to debug Polyfill Errors in Angular
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Polyfills are necessary for the compatibility across the browsers to provide the feasibility to run modern javascript in old browsers or environments that do not natively support them.
These errors usually occur when the app depends on browser-specific features that are not available in certain browsers or environments without additional support. Developers can debug these errors using listed steps -
Understand the error message
For the errors that typically state that a function or a Feature is not defined, for example, Object.assign is not a function or a Promise is an undefined feature; the feature checks or Console Checks can aid in the search .
Moreover, IE and other older versions of web browsers are known to have polyfill related problems, one can always pinpoint a feature or function to their alliances, this can help narrow the problem.
Identify Missing Features
Use tools like caniuse.com to verify browser support for the feature in question.If the feature is unsupported, a polyfill might be needed to configure in the application.
Check polyfills.ts File
In Angular, polyfills.ts manages the polyfills required by the app.
Common polyfills:
import 'core-js/es6/promise'; // For older browsersimport 'core-js/es6/map';import 'core-js/es6/set';import 'core-js/es7/array';import 'zone.js/dist/zone'; // Angular-specific
Check Browser Compatibility Mode
Ensure that the app is not running in IE compatibility mode if IE11 support is intended.
Add the meta tag in index.html to disable compatibility mode:
<meta http-equiv="X-UA-Compatible" content="IE=edge">
Update browserslist Configuration
The browserslist file in the project specifies the browsers that your app supports. Ensure it includes:
> 0.5%last 2 versionsFirefox ESRnot deadIE 11 // If supporting Internet Explorer Install and Update Dependencies
Some polyfills require external packages:
npm install --save core-jsnpm install --save classlist.jsnpm install --save web-animations-js
Use a Modern Build Configuration
Starting with Angular 9+, differential loading handles older browsers differently. Ensure your angular.json has correct configurations for es2015 and es5 builds.
Custom Polyfills
If a specific feature is still missing, manually add polyfills:
if (!String.prototype.includes) { String.prototype.includes = function (search, start) { return this.indexOf(search, start) !== -1; };}Check for Third-Party Library Issues
Some libraries may require polyfills. Check the documentation of third-party libraries to see if specific polyfills are recommended.
Test in Target Browsers
Use browser developer tools or tools like BrowserStack for testing across different versions and environments.
By following these steps, you can systematically diagnose and fix polyfill errors in Angular applications.
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