本篇只是简单分析 Fiber。

Fiber 调度与更新函数调用栈：（react-conciler\src\ReactFiberWorkLoop.js）

fiber-call-stack.png

模拟Fiber工作流程

NodeJS环境下，运行该JS文件： node xxx.js 即可看到输出结果

• 定义对象

 const a1 = {name: 'a1', child: null, sibling: null, return: null};
 const b1 = {name: 'b1', child: null, sibling: null, return: null};
 const b2 = {name: 'b2', child: null, sibling: null, return: null};
 const b3 = {name: 'b3', child: null, sibling: null, return: null};
 const c1 = {name: 'c1', child: null, sibling: null, return: null};
 const c2 = {name: 'c2', child: null, sibling: null, return: null};
 const d1 = {name: 'd1', child: null, sibling: null, return: null};
const d2 = {name: 'd2', child: null, sibling: null, return: null};

• 定义对象之间的关系

a1.child = b1;
b2.child = c1;
b3.child = c2;
c1.child = d1;

b1.sibling = b2;
b2.sibling = b3;
d1.sibling = d2;

b3.return = a1;
c1.return = b2;
c2.return = b3;
d2.return = c1;

• 给出对象之间的遍历顺序

/****************************************
 *
 *    a1 <------------------
 *    |                    |
 *    b1 ----> b2 -------> b3 <--
 *        |    |           |    |
 *         --- c1 <---     c2 ---
 *             |     |
 *             d1 -> d2
 *
 *    DFS(Deep First Search) 深度优先搜索
 *
 ****************************************/

• 具体的工程流程如下：

let nextUnitOfWork = a1;
workLoop();

function workLoop() {
    while(nextUnitOfWork !== null) {
        nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
    }
}

function performUnitOfWork(workInProgress) {
    // first work for child
    let next = beginWork(workInProgress);
    if (next === null) {
        // then work for sibling
        next = completeUnitOfWork(workInProgress);
    }
    return next;
}

function beginWork(workInProgress) {
    console.log('[performUnitOfWork][beginWork] => ' + workInProgress.name);
    return workInProgress.child;
}

function completeUnitOfWork(workInProgress) {
    while(true) {
        let sibling = workInProgress.sibling;
        let ret = workInProgress.return;
        completeWork(workInProgress);

        if (sibling) {
            return sibling;
        } else if (ret) {
            workInProgress = ret;
            continue;
        } else {
            return null;
        }
    }
}

function completeWork(workInProgress) {
    console.log('[completeUnitOfWork][completeWork] => ' + workInProgress.name + '\n');
    return null;
}

纸画流程图（DFS for Fiber Workflow）

simulate-fiber-workflow.jpeg