Layer (type)                 Output shape              Param #
=================================================================
dense_Dense1 (Dense)         [null,1]                  2
=================================================================
Total params: 2
Trainable params: 2
Non-trainable params: 0

const tf = require("@tensorflow/tfjs-node")

function convert(c){
    return (c*1.8)+32 // Convert celsius to fahrenheit
}

var celsius = []
var fahrenheit = []

for (let i = 0; i < 20; i++) {
    var r = 100; // Keeping this only value to ensure that Tf knows the answer I also have tried with 20 different values but doesn't work
    celsius.push([r]) // Shape [20,1]
    fahrenheit.push([convert(r)]) // Push the answer (212) to the fahrenheit array
}

var model = tf.sequential();
model.add(tf.layers.dense({inputShape:[1], units: 1}))

async function trainModel(model, inputs, labels) {
    // Prepare the model for training.
    model.compile({
      optimizer: tf.train.adam(),
      loss: tf.losses.meanSquaredError,
      metrics: ['accuracy'], // Accuracy = 0
    });

    model.summary();

    const epochs = 500;

    return await model.fit(inputs, labels, {
      epochs,
      batchSize: 20,
      verbose: false // Nothing interesting with verbose
    });
  }

c = tf.tensor(celsius)
f = tf.tensor(fahrenheit)

var training = trainModel(model, c, f)

training.then(function(args){
    var prediction = model.predict(tf.tensor([[100]]));
    prediction.print(); // Prints a random number
    console.log("Real answer = "+convert(100))
})

Tensor
     [[65.9411697],]
Real answer = 212

const tf = require("@tensorflow/tfjs-node")
const nr_epochs=500;

function convert(c){
  return (c*1.8)+32 // Convert celsius to fahrenheit
}


var celsius = []
var fahrenheit = []

for (let i = 0; i < 100; i++) {
  var r = 100; // Keeping this only value to ensure that Tf knows the answer
  celsius.push(i) // Shape [20,1]
  fahrenheit.push(convert(i)) // Push the answer (212) to the fahrenheit array
}

let train = async (xy, ys) => {
  const model = tf.sequential();

  model.add(tf.layers.dense({units: 1, inputShape: [1]}));

  model.compile({loss: 'meanSquaredError', optimizer: 'sgd'});
  await model.fit(xs,ys,{epochs: nr_epochs})
  return model;
}

let predict =  (model, n) => {
  const predicted =  model.predict(tf.tensor2d([n],[1,1]));
  return predicted;
}

const xs = tf.tensor2d(celsius.slice (0,15), [15,1]);
const ys = tf.tensor2d(fahrenheit.slice (0,15), [15,1]);
(async () => {
  let trained = await train (xs,ys);
  for (let n of [4,6,12]) {
    let predicted = predict (trained, n).dataSync ();
    console.log (`Value: ${n} Predicted: ${predicted [0]}`)
  }
})()

Value: 4 Predicted: 38.01055908203125
Value: 6 Predicted: 42.033267974853516
Value: 12 Predicted: 54.101402282714844