Build your own React
构建 简化版 react
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
</head>
<body>
<button id="btn">Update</button>
<div id="root"></div>
<script src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
<script type="text/babel">
function createElement(type, props, ...children) {
return {
type,
props: {
...props,
children: children.map((child) => {
return typeof child === "object"
? child
: createTextElement(child);
}),
},
};
}
function createTextElement(text) {
return {
type: "TEXT_ELEMENT",
props: {
nodeValue: text,
children: [],
},
};
}
function createDom(fiber) {
const dom =
fiber.type === "TEXT_ELEMENT"
? document.createTextNode("")
: document.createElement(fiber.type);
updateDom(dom, {}, fiber.props);
return dom;
}
const isEvent = (key) => key.startsWith("on");
const isProperty = (key) => key !== "children";
const isNew = (prev, next) => (key) => prev[key] !== next[key];
const isGone = (prev, next) => (key) => !(key in next);
function updateDom(dom, prevProps, nextProps) {
Object.keys(prevProps)
.filter(isEvent)
.filter(
(key) => !(key in nextProps) || isNew(prevProps, nextProps)(key)
)
.forEach((name) => {
const eventType = name.toLowerCase().substring(2);
dom.removeEventListener(eventType, prevProps[name]);
});
Object.keys(prevProps)
.filter(isProperty)
.filter(isGone(prevProps, nextProps))
.forEach((name) => {
dom[name] = "";
});
Object.keys(nextProps)
.filter(isProperty)
.filter(isNew(prevProps, nextProps))
.forEach((name) => {
dom[name] = nextProps[name];
});
Object.keys(nextProps)
.filter(isEvent)
.filter(isNew(prevProps, nextProps))
.forEach((name) => {
const eventType = name.toLocaleLowerCase().substring(2);
dom.addEventListener(eventType, nextProps[name]);
});
}
function commitRoot() {
deletions.forEach(commitWork);
commitWork(wipRoot.child);
currentRoot = wipRoot;
wipRoot = null;
}
function commitWork(fiber) {
if (!fiber) return;
let domParentFiber = fiber.parent;
while (!domParentFiber.dom) {
domParentFiber = domParentFiber.parent;
}
const domParent = domParentFiber.dom;
if (fiber.effectTag === "PLACEMENT" && fiber.dom !== null) {
domParent.appendChild(fiber.dom);
} else if (fiber.effectTag === "UPDATE" && fiber.dom !== null) {
updateDom(fiber.dom, fiber.alternate.props, fiber.props);
} else if (fiber.effectTag === "DELETION") {
commitDeletion(fiber, domParent);
}
commitWork(fiber.child);
commitWork(fiber.sibling);
}
function commitDeletion(fiber, domParent) {
if (fiber.dom) {
domParent.removeChild(fiber.dom);
} else {
commitDeletion(fiber.child, domParent);
}
}
function render(element, container) {
wipRoot = {
dom: container,
props: {
children: [element],
},
alternate: currentRoot,
};
deletions = [];
nextUnitOfWork = wipRoot;
}
let nextUnitOfWork = null;
let currentRoot = null;
let wipRoot = null;
let deletions = null;
function workLoop(deadline) {
let shouldYield = false;
while (nextUnitOfWork && !shouldYield) {
nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
shouldYield = deadline.timeRemaining() < 1;
}
requestIdleCallback(workLoop);
if (!nextUnitOfWork && wipRoot) {
commitRoot();
}
}
requestIdleCallback(workLoop);
function performUnitOfWork(fiber) {
const isFunctionComponent = fiber.type instanceof Function;
if (isFunctionComponent) {
updateFunctionComponent(fiber);
} else {
updateHostComponent(fiber);
}
if (fiber.child) return fiber.child;
let nextFiber = fiber;
while (nextFiber) {
if (nextFiber.sibling) return nextFiber.sibling;
nextFiber = nextFiber.parent;
}
}
let wipFiber = null;
let hookIndex = null;
function updateFunctionComponent(fiber) {
wipFiber = fiber;
hookIndex = 0;
wipFiber.hooks = [];
const children = [fiber.type(fiber.props)];
reconcileChildren(fiber, children);
}
function useState(initial) {
const oldHook =
wipFiber.alternate &&
wipFiber.alternate.hooks &&
wipFiber.alternate.hooks[hookIndex];
// 从alternate中取出上一次的hook.
const hook = {
state: oldHook ? oldHook.state : initial,
queue: [],
};
const actions = oldHook ? oldHook.queue : [];
actions.forEach((action) => {
hook.state = action(hook.state);
});
const setState = (action) => {
hook.queue.push(action);
(wipRoot = {
dom: currentRoot.dom,
props: currentRoot.props,
alternate: currentRoot,
}),
(nextUnitOfWork = wipRoot);
deletions = [];
};
wipFiber.hooks.push(hook);
hookIndex++;
return [hook.state, setState];
}
function updateHostComponent(fiber) {
if (!fiber.dom) fiber.dom = createDom(fiber);
reconcileChildren(fiber, fiber.props.children);
}
function reconcileChildren(wipFiber, elements) {
let index = 0;
let oldFiber = wipFiber.alternate && wipFiber.alternate.child;
let prevSibling;
while (index < elements.length || oldFiber != null) {
const element = elements[index];
let newFiber = null;
// compare oldFiber to element
const sameType =
oldFiber && element && element.type === oldFiber.type;
if (sameType) {
// Update the node
newFiber = {
type: oldFiber.type,
props: element.props,
dom: oldFiber.dom,
parent: wipFiber,
alternate: oldFiber,
effectTag: "UPDATE",
};
}
if (element && !sameType) {
// Add this node
newFiber = {
type: element.type,
props: element.props,
dom: null,
parent: wipFiber,
alternate: null,
effectTag: "PLACEMENT",
};
}
if (oldFiber && !sameType) {
// Delete the oldFiber's node
oldFiber.effectTag = "DELETION";
deletions.push(oldFiber);
}
if (oldFiber) oldFiber = oldFiber.sibling;
if (index === 0) {
wipFiber.child = newFiber;
} else if (element) {
prevSibling.sibling = newFiber;
}
prevSibling = newFiber;
index++;
}
}
const Didact = {
createElement,
render,
useState,
};
/** @jsx Didact.createElement */
function Counter() {
const [state, setState] = Didact.useState(1);
const [num, setNum] = Didact.useState(1);
return (
<div>
<h1 onClick={() => setState((c) => c + 1)}>Count: {state}</h1>
<h1 onClick={() => setNum((c) => c + 1)}>Num: {num}</h1>
</div>
);
}
const container = document.getElementById("root");
Didact.render(<Counter></Counter>, container);
</script>
</body>
</html>
