# Javascript.info 2.12 Nullish coalescing operator '??' (9/16)

ref: https://javascript.info/nullish-coalescing-operator

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polyfills 自動補完函式庫

A polyfill, or polyfiller, is a piece of code (or plugin) that provides the technology that you, the developer, expect the browser to provide natively. Flattening the API landscape if you will.

* 要注意瀏覽器支援度

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### Nullish coalescing operator ??

空值合併

1. provides a short syntax for selecting a first “defined” variable from the list.

括弧裡面的東西是最優先執行的

2. Due to safety reasons, it’s forbidden to use ?? together with && and || operators.

??比較少用
通常是去比較 null 和 defined

常用在判斷0的時候


###### tags: `Javascript`
{%hackmd BJrTq20hE %}