Explain why componentDidMount is a better place to make an ajax request

In the docs, in componentWillMount section section it says:

Avoid introducing any side-effects or subscriptions in this method

And in the componentDidMount section:

If you need to load data from a remote endpoint, this is a good place to instantiate the network request

Which for me is confusing because I won't like to wait for the component to be mounted to dispatch an ajax call to fulfill the component data dependencies. I would like to do it as soon as possible, like in the constructor, not even in componentWillMount.

Clearly you may have a reason why you say this in the docs, I might be not seeing the bigger picture. So it will be nice if you can explain a bit more in detail or point me in the direction of where I can find the reason.

閱讀 React 文件中連結的 componentWillMount 和 componentDidMount 部分，以及周圍關於生命週期的指引。說明文件為什麼建議在 componentDidMount 中開始遠端請求，並回應需要等到掛載完成這項疑慮；當時機指引和理由都清楚時，該 issue 就完成了。