javascript - What does "function(): any{" mean - Stack Overflow

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I saw this snippet here:

render: function(): any {
  var thread = this.state.thread;
  var name = thread ? thread.name : "";
  var messageListItems = this.state.messages.map(getMessageListItem);
  return (
    <div className="message-section">
    <h3 className="message-thread-heading">{name}</h3>
// ...

What does the function(): any{ part in the first line mean?

Apologies if this has been asked before, but it's really hard to search this, particularly when you don't know what it's called.

I saw this snippet here:

render: function(): any {
  var thread = this.state.thread;
  var name = thread ? thread.name : "";
  var messageListItems = this.state.messages.map(getMessageListItem);
  return (
    <div className="message-section">
    <h3 className="message-thread-heading">{name}</h3>
// ...

What does the function(): any{ part in the first line mean?

Apologies if this has been asked before, but it's really hard to search this, particularly when you don't know what it's called.

• javascript

Share Improve this question Follow edited Apr 12, 2022 at 2:37 Alexander O'Mara 60.6k1919 gold badges172172 silver badges181181 bronze badges asked May 30, 2015 at 4:17 Dave PileDave Pile 5,77444 gold badges3737 silver badges5151 bronze badges 4

• Is this using a framework? – Cristian Cavalli Commented May 30, 2015 at 4:21
• The snippet is part of reactjs but the particular line is plain javascript (I expect its some ES6 thing). Render is a member of an object – Dave Pile Commented May 30, 2015 at 4:23
• 5 This isn't Javascript code. It is "flowtype", some sort of pre-processor. – Agamemnus Commented May 30, 2015 at 4:24
• Perhaps any is it's return / accepted argument type? I'm kinda just looking at flow now. – Cristian Cavalli Commented May 30, 2015 at 4:26

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2 Answers 2

Sorted by: Reset to default 10

That's not a part of JavaScript, it's an extra feature added by Flow, a JavaScript preprocessor. TypeScript also has a similar feature.

Essentially, Flow adds a type-checking feature, and to use it you add type-hinting to symbols. In this case, : any is a type hint for the render method, meaning the method could return any type.

Excerpt from the type annotations docs for any:

any is a special type annotation that represents the universal dynamic type. any can flow to any other type, and vice-versa. any is basically the "get out of my way, I know what I am doing" annotation. Use it when Flow is getting in your way, but you know your program is correct.

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A fun little side note, there was a proposed feature in the now-abandoned ES4 draft for type hinting that was very similar to this. As far as I know, it was only ever implemented in the ES-derived ActionScript 3.

Very simple and straightforward answer is function(): any will return any type of data.

It means you can return string boolean number or any type of data you want from that function.

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