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One way to ensure that the state is evaluated before the first render in Gatsby is to use the getDerivedStateFromProps method. This method is called before the component is mounted and can be used to set the state based on the props.

Here's an example:

import React, { Component } from "react"

class MyComponent extends Component {
  static getDerivedStateFromProps(props, state) {
    // evaluate the state here based on props
    const newState = {
      // ... computed state based on props
    }
    return newState
  }

  constructor(props) {
    super(props)
    this.state = {
      // initialize state here if necessary
    }
  }

  render() {
    // render component using state
    return (
      // ...
    )
  }
}

export default MyComponent

In this example, the getDerivedStateFromProps method is called before the component is mounted and returns the computed state based on the props. The state is then initialized in the constructor and used to render the component.