F - WithConstructor.tsx

// Example

export class ConstructorComponent extends React.Component<{ start: number }, { count: number }> {
  // React Components takes `props` as a constructor argument. You can set default state here as well.
  constructor(props) {
    super(props);
    this.state = { count: props.start };
    this.count = countService.count();
    this.positiveCount = this.count.pipe(filter(c => c > 0));
  }
}

Good - NoConstructor.tsx

// Better (imo) Example

import * as React from 'react';

export class NoConstructorComponent extends React.Component<{ start: number }, { count: number }> {
  state = { count: this.props.start };
  count = countService.count();
  positiveCount = this.count.pipe(filter(c => c > 0));
}