Variables, Built-in types, Comments

Variables

Here’s an example of creating a variable and initializing it:

mapstructure

mapstructure is a Go library for decoding generic map values to structures and vice versa, while providing helpful error handling.

This library is most useful when decoding values from some data stream (JSON, Gob, etc.) where you don’t quite know the structure of the underlying data until you read a part of it. You can therefore read a map[string]interface{} and use this library to decode it into the proper underlying native Go structure.

1. Hello World

The smallest React example looks like this:

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ReactDOM.render(
  <h1>Hello, world!</h1>,
  document.getElementById('root')
);

It displays a heading saying “Hello, world!” on the page.

Introducing JSX

Consider this variable declaration:

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const element = <h1>Hello, world!</h1>;

It is called JSX, and it is a syntax extension to JavaScript. We recommend using it with React to describe what the UI should look like. JSX may remind you of a template language, but it comes with the full power of JavaScript.

Rendering Elements

Elements are the smallest building blocks of React apps.

Components and Props

Components let you split the UI into independent, reusable pieces, and think about each piece in isolation. This page provides an introduction to the idea of components. You can find a detailed component API reference here - https://reactjs.org/docs/react-component.html.

Conceptually, components are like JavaScript functions. They accept arbitrary inputs (called “props”) and return React elements describing what should appear on the screen.

Function and Class Components

The simplest way to define a component is to write a JavaScript function:

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function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

This function is a valid React component because it accepts a single “props” (which stands for properties) object argument with data and returns a React element. We call such components “function components” because they are literally JavaScript functions.

You can also use an ES6 class - https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Classes to define a component:

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class Welcome extends React.Component {
  render() {
    return <h1>Hello, {this.props.name}</h1>;
  }
}

The above two components are equivalent from React’s point of view.

Rendering a Component

Previously, we only encountered React elements that represent DOM tags:

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const element = <div />;

However, elements can also represent user-defined components:

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const element = <Welcome name="Sara" />;

When React sees an element representing a user-defined component, it passes JSX attributes and children to this component as a single object. We call this object “props”.

For example, this code renders “Hello, Sara” on the page:

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function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

const element = <Welcome name="Sara" />;
ReactDOM.render(
  element,
  document.getElementById('root')
);

Try it on CodePen - https://reactjs.org/redirect-to-codepen/components-and-props/rendering-a-component

Let’s recap what happens in this example:

• We call ReactDOM.render() with the <Welcome name="Sara" /> element.

• React calls the Welcome component with {name: 'Sara'} as the props.

• Our Welcome component returns a <h1>Hello, Sara</h1> element as the result.

• React DOM efficiently updates the DOM to match <h1>Hello, Sara</h1>.

Note: Always start component names with a capital letter.

React treats components starting with lowercase letters as DOM tags. For example,

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function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

function App() {
  return (
    <div>
      <Welcome name="Sara" />
      <Welcome name="Cahal" />
      <Welcome name="Edite" />
    </div>
  );
}

ReactDOM.render(
  <App />,
  document.getElementById('root')
);

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function Comment(props) {
  return (
    <div className="Comment">
      <div className="UserInfo">
        <img className="Avatar"
          src={props.author.avatarUrl}
          alt={props.author.name}
        />
        <div className="UserInfo-name">
          {props.author.name}
        </div>
      </div>
      <div className="Comment-text">
        {props.text}
      </div>
      <div className="Comment-date">
        {formatDate(props.date)}
      </div>
    </div>
  );
}

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function Avatar(props) {
  return (
    <img className="Avatar"
      src={props.user.avatarUrl}
      alt={props.user.name}
    />
  );
}

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function Comment(props) {
  return (
    <div className="Comment">
      <div className="UserInfo">
        <Avatar user={props.author} />
        <div className="UserInfo-name">
          {props.author.name}
        </div>
      </div>
      <div className="Comment-text">
        {props.text}
      </div>
      <div className="Comment-date">
        {formatDate(props.date)}
      </div>
    </div>
  );
}

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function UserInfo(props) {
  return (
    <div className="UserInfo">
      <Avatar user={props.user} />
      <div className="UserInfo-name">
        {props.user.name}
      </div>
    </div>
  );
}

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function Comment(props) {
  return (
    <div className="Comment">
      <UserInfo user={props.author} />
      <div className="Comment-text">
        {props.text}
      </div>
      <div className="Comment-date">
        {formatDate(props.date)}
      </div>
    </div>
  );
}

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function sum(a, b) {
  return a + b;
}

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function withdraw(account, amount) {
  account.total -= amount;
}

5. State and Lifecycle

This page introduces the concept of state and lifecycle in a React component. You can find a detailed component API reference here - https://reactjs.org/docs/react-component.html.

Handling Events

Handling events with React elements is very similar to handling events on DOM elements. There are some syntax differences:

• React events are named using camelCase, rather than lowercase.

• With JSX you pass a function as the event handler, rather than a string.

Hidden Bar

Hidden Bar lets you hide menu bar items to give your Mac a cleaner look.

Talking-Golang (Go) Index

Types

Variable Declaration and Initialization

(TODO) new() VS make()

(TODO) Zero Values

Type Assertions

Type Twitches

(TODO) Type Conversion

Naming

(TODO) Errors