42 lines
1.2 KiB
Markdown
42 lines
1.2 KiB
Markdown
---
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title: Polyfill.io
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category: JavaScript libraries
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updated: 2018-08-20
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intro: |
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[Polyfill.io](https://polyfill.io) is a service that serves JavaScript polyfills.
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---
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## Usage
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### Default usage
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```html
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<script src="https://cdn.polyfill.io/v2/polyfill.min.js"></script>
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```
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{: .-wrap}
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This is the default script for Polyfill.io.
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### References
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* [API example](https://polyfill.io/v2/docs/api) _(polyfill.io)_
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* [List of features](https://polyfill.io/v2/docs/features) _(polyfill.io)_
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## Optimized
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### For modern browsers
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```html
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<script>if(!(window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdn.polyfill.io/v2/polyfill.min.js"></scr'+'ipt>')}</script>
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```
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This only includes polyfill.io when necessary, skipping it for modern browsers for faster load times.
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### Extra features
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```html
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<script>if(!(window.fetch&&window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=default,fetch"></scr'+'ipt>')}</script>
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```
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This is the same as the previous, but also adds a polyfill for `window.fetch()`. We add a `window.fetch` check and loads the additional `fetch` feature.
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