保锦

1. ` 4` 2. ` arr=arr.filter(item=>{ return true }) ` 3. ` let arr2=[1, NaN, NaN]` 4. `let arr3=arr.concat(arr2)` 5. `Array.from(new Set(arr3))`

[demo](https://codepen.io/baojin/pen/xoXoOd) ```html 按钮 按钮 按钮 ``` ```SCSS /* zxx: 下次请粘贴编译好的CSS */ .btn_container { display: flex; flex-wrap: nowrap; /* zxx: 可以去掉 */ .btn_item { + .btn_item { margin-left: 1rem; } &:focus...

1. ```javascript let NodeList_A= document.querySelectorAll("a") ``` 2. ```javascript // zxx: 也会被选中 let NodeList_Href= document.querySelectorAll("[href]") ``` 3.1 ```javascript NodeList_Hrdef.forEach((item)=>{ let temp=item.href; let reg=/^javascript/ if(reg.test(temp)){ item.setAttribute("role", "button") } }) ``` 3.2 ```javascript...