Do you really know react portals

Song in the clouds 2020-11-09 11:30:26
really know react portals

In the past, when writing global masks , I usually use fixed location , The sample code is as follows :

.modal {
position: fixed;
left: 0;
right: 0;
top: 0;
bottom: 0;
background: black;

This is to implement the global mask layer ,modal The content is controlled by itself . But there's a problem with that , As follows :

You can see that the contents of this pop-up window are not in body The next floor , It's nested in layers dom inside , There are two disadvantages :

  1. DOM The structure is not elegant enough
  2. The style of the parent component may affect the style of the child component

Here's a real case , Colleagues also use it fixed The global pop-up window is generated by positioning , But found that the button click can not change the pop-up window display , Then I found that I wrote a wonderful code , The code looks like this :

<!-- Here are the subcomponents -->
return (
<span>toggle visible</span>
<modal visible={visible}></modal>

Then I found that the button can't be controlled modal Show hidden , Because of this button Seriously affected modal act .
This kind of problem is very difficult to solve , You don't know what wonderful code the user wrote , At this time, consider other ways to avoid this problem . In user use modal When , This modal Of dom It is actually mounted under the current component , Imagine if you put this DOM Directly inserted into the body Is it possible to avoid these problems
fortunately React Provides the ability to , So let's talk about that react Provided in the child node rendering outside of the parent component DOM Node Portal

Portal Introduce

Portal Be able to render child components to other than the parent component DOM Trees , It is usually used in scenarios where a child component needs to be detached from the parent component's container , There are the following scenarios :

  • Dialog Dialog box
  • Tooltip Text prompt
  • Popover pop-up
  • Loader overall situation loader

Here's how he uses it :


The first parameter (child) Is anything that can be rendered React Subelement , For example, an element , String or fragment. The second parameter (container) It's a DOM Elements .
Here's how to use react.createPortal A simple example of :

const Modal = ({message, visible, onClose, children}) => {
if (!visible) return null;
return ReactDOM.createPortal(
<div class="modal">
<span className="message">{message}</span>
<button onClick={onClose}>Close</button>
, domNode)

although portal Break away from the container restrictions of the parent component , But his performance and normal React Components are consistent . Can also receive props and context. This is because portal There is still react In the hierarchical tree of .

Why Portal

Just like a case mentioned at the beginning of the article , In a component, we need to use modal Popup , Most of the time we can use fixed Positioning allows the pop-up window to be displayed globally , But in special cases , This modal The pop-up window may display abnormal . So at this time, if we use portal In a direct way modal Of dom The structure is separated from the container of the parent component , You can avoid this problem .

const Modal = ({message, isOpen, onClose, children}) => {
if (!isOpen) return null;
return ReactDOM.createPortal(
<div className="modal">
<button onClick={onClose}>Close</button>
, document.body)
function Component() {
const [open, setOpen] = useState(false)
return (
<div className="component">
<button onClick={() => setOpen(true)}></button>
message="Hello World!"
onClose={() => setOpen(false)}

The above code guarantees that , No matter how deep the subcomponents are nested , This modal Can and root Same level . Use chrome Check dom structure , You can see the following structure

Use Portal Points for attention

In the use of Portal When , You need to know that even though Portal Can be placed in DOM Anywhere in the tree , But behavior and ordinary React Component behavior is consistent . because portal Still exists in React Trees , And with the DOM Trees It's not about the position in , So whether its child node is portal, image context Such features are unchangeable .
Here's a summary of some considerations .

  1. Event Bubbling : A from portal Internally triggered events will bubble until they contain React The ancestors of trees , Even if these elements are not DOM Trees The ancestors of .
  2. Life cycle : Even through Portal Created elements , This element still has its life cycle, such as componentDidMount wait
  3. scope : Portal Will only affect HTML The structure of will not affect React Tree structure
  4. Mount node : When using Portal You have to define a real DOM Node as Portal The mount entry of the component


When we need to be in normal DOM When rendering sub components outside the structure ,React Portal Very useful , You don't have to pass it React The component tree hierarchy destroys the default behavior of event propagation , This is rendering, like pop-up window 、 Tips are very useful

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