生命周期方法在React的源代码中定义在哪里？

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { data: null };
  }

  componentDidMount() {
    // 组件挂载后执行，例如获取数据
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => this.setState({ data }));
  }

  shouldComponentUpdate(nextProps, nextState) {
    // 根据条件决定是否更新组件
    return this.state.data !== nextState.data;
  }

  componentWillUnmount() {
    // 组件卸载前执行清理工作
    console.log('Component is unmounting');
  }

  render() {
    return (
      <div>
        {this.state.data ? <p>{this.state.data}</p> : <p>Loading...</p>}
      </div>
    );
  }
}

export default MyComponent;

componentDidMount() {
  this.isMounted = true;
  fetch('https://api.example.com/data')
    .then(response => response.json())
    .then(data => {
      if (this.isMounted) {
        this.setState({ data });
      }
    });
}

componentWillUnmount() {
  this.isMounted = false;
}