Js can’t get info from fetching

So I’m trying to create a small molarity concentration calculator for my lab, which has some chemicals we often use. When I try to fetch the chemicals.json, the web can fetch the JSON file but can not process the calculation.

<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <label for="chemical_select">選擇化學物質:</label>
    <select id="chemical_select">
        <option value="APTES">APTES</option>
        <option value="Cyclopropylamine">Cyclopropylamine</option>
    <label for="solvent_volume">溶劑體積 (ml):</label>
    <input type="number" id="solvent_volume" placeholder="輸入溶劑體積"><br><br>
    <label for="solution_concentration">溶液濃度 (mM):</label>
    <input type="number" id="solution_concentration" placeholder="輸入溶液濃度"><br><br>
    <button onclick="calculateChemical()">計算</button><br><br>
    <p id="chemical_use">需加入化學物質 (ul): </p>

        function calculateChemical() {
            var selectedChemical = document.getElementById("chemical_select").value;
            var solventVolume = parseFloat(document.getElementById("solvent_volume").value);
            var solutionConcentration = parseFloat(document.getElementById("solution_concentration").value);

                .then(response => response.json())
                .then(data => {
                    var chemicals = data;

                    if (chemicals[selectedChemical] && chemicals[selectedChemical]['Mweight'] !== undefined && chemicals[selectedChemical]['Density'] !== undefined) {
                        var chemicalMw = chemicals[selectedChemical]['Mweight'];
                        var chemicalDensity = chemicals[selectedChemical]['Density'];

                        var chemicalUseInMl = (solutionConcentration * solventVolume * chemicalMw) / (chemicalDensity * 1000000 - solutionConcentration * chemicalMw);
                        var chemicalUseInUl = (chemicalUseInMl * 1000).toFixed(2);

                        document.getElementById("chemical_use").innerText = "需加入化學物質 (" + selectedChemical + "):" + chemicalUseInUl + " ul";
                    } else {
                .catch(error => console.error('Fetch Error:', error));

I added an if/else function to see what’s wrong with the code, and it shows that “無法找到化學物質資訊” which means Could not find out chemical information.