Why Do React Component Names Need to Start with a Capital Letter?

Component Names in React: Capitalization Conundrum

When working with ReactJS, it's common to encounter a peculiar behavior regarding component names. Unlike HTML elements, React components must begin with capital letters. This distinction arises from a fundamental architectural decision in React's underlying architecture.

React leverages JSX (JavaScript XML) to define UI elements. In JSX, lower-case tag names are interpreted as HTML tags, while upper-case tag names indicate React components. This distinction is made because HTML tags interact with the browser's native DOM, while React components are custom elements managed by React's internal reconciliation engine.

Consider the following example, where the component name begins with a lowercase letter:

var fml = React.createClass({
  render: function () {
    return <a href='google.com'>Go</a>;
  }
});

React.render(<fml />, document.body);

This code will not render the intended element. Instead, React interprets "fml" as an HTML tag and attempts to match it to a corresponding element in the DOM. However, since "fml" doesn't exist as a valid HTML tag, the result is a blank page.

When the component name is changed to uppercase, as in:

var Fml = React.createClass({
  render: function () {
    return <a href='google.com'>Go</a>;
  }
});

React.render(<Fml />, document.body);

React recognizes "Fml" as a component and initializes it, allowing the rendered element to appear on the page.

In summary, React component names must begin with uppercase letters to differentiate them from HTML tags. This distinction ensures proper component management and the correct rendering of the user interface.

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