function bmi(weight, height) {

  // Your BMI is weight / height squared
  let result = weight / height ** 2;

  // Our array of results
  let weightClasses = [
    18.5, 'Underweight', 
    25.0, 'Normal', 
    30.0, 'Overweight', 
    30.1, 'Obese'
    ];

  // If you've reached the highest BMI number, return the last weight class
  for (let i = 0; i < weightClasses.length; i+=2) {
    if (i === weightClasses.length - 2) {
      return weightClasses[weightClasses.length - 1];
    }

    // Return the name of the appropriate weight class
    if (result < weightClasses[i]) {
      return weightClasses[i+1];
    }
  }
}

Try it yourself - Codewars Source

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