<ul>
<li>?? operator will coerce undefined and null values to false and other values to true.</li>
</ul>
<pre><code class="lang-javascript">let propertyCheck = person.age ?? 0;
let objectAndPropertyCheck = (person ?? {}).age ?? 0;
// or
let objectAndPropertyCheck2 = person?.age ?? 0;
// the ? character will stop evaluating an expression if the value 
// it is applied to is null or undefined.
</code></pre>
<ul>
<li>select properties</li>
</ul>
<pre><code class="lang-javascript">let person = {
 name: 'psi',
 age: 20,
}
let { name, ...someProperties } = person;
console.log(`Selected: ${JSON.stringify(someProperties)}`);
// Selected: {"age":20}
</code></pre>
<ul>
<li>this</li>
</ul>
<pre><code class="lang-javascript">// node环境下，最外层的对象是global，但最外层的this并不是全局对象global，
// 而是module.exports 
console.log(module.exports === this); //true 
// 但从最外层调用函数，将会使得函数中的this指向global。

//浏览器环境下，最外层的对象是windows,并且最外层的this就是windows。
</code></pre>

* **?? operator** will coerce **undefined** and **null** values to false and other values to true.
    

```javascript
let propertyCheck = person.age ?? 0;
let objectAndPropertyCheck = (person ?? {}).age ?? 0;
// or
let objectAndPropertyCheck2 = person?.age ?? 0;
// the ? character will stop evaluating an expression if the value 
// it is applied to is null or undefined.
```

* select properties
    

```javascript
let person = {
    name: 'psi',
    age: 20,
}
let { name, ...someProperties } = person;
console.log(`Selected: ${JSON.stringify(someProperties)}`);
// Selected: {"age":20}
```

* this
    

```javascript
// node环境下，最外层的对象是global，但最外层的this并不是全局对象global，
// 而是module.exports 
console.log(module.exports === this); //true 
// 但从最外层调用函数，将会使得函数中的this指向global。

//浏览器环境下，最外层的对象是windows,并且最外层的this就是windows。
```

Javascript snippets