Did search and found several StackOverflow answer use componentWillMount. However, Facebook itself uses componentDidMount to call jQuery Ajax. Both works!
How do you decide which one to use? Is there recommended way for meteor specific? I can’t find on Meteor Guide.
Prefer componentWillMount, unless you need access to the rendered DOM, in which case use componentDidMount. This is, I think, a pure React question, so you can find better guidance there.
Have you tried it (ajax from constructor) and liked it, or are you just saying what you’ve heard? I saw the same buzz, tried it, didn’t like it. Most significantly, this.props is undefined in the constructor, so if the ajax call is dependent on, say, a passed-in key of an object to be gotten via ajax, you’re SOL. Similarly, if you’re using Redux, no props means no dispatch (at least by normal means). If any of the folks who “hearted” this have better guidance on when and why the constructor’s better, or on workarounds for the issues I raised above, I’d be happy to hear - all I have is more of this kind of vague “I heard that” second-hand recommendation, with no motivation and no warning about the gotchas.