JavaScript + HTML: How to write a string literal to a JSON file?

Question

I am trying to program a recipe website in JavaScript. The recipe editor is able to load in contents from a JSON file by creating HTML elements to store them. I want it to be able to then construct a string literal from the data as it is changed by the user, and write it back to the JSON file.

The file's path is "/JS_Scripts/Recipes/JSON/test.json"

function writeToRecipeFile(filePath)
{
    let formData = new FormData();
    let recipeFileContents = 
    `{
        "image": "",
        "title": "${document.getElementById("titleInput").value}",
        "description": "${document.getElementById("descriptionInput").innerText}",
        "ingredients": [`

    //Add ingredients array
    for(i = 1; i <= ingredientCount; i++)
    {
        recipeFileContents = recipeFileContents + 
        `[
            "${document.getElementById("ingredientType"+i).value}",
            ${document.getElementById("ingredientAmount"+i).value},
            "${document.getElementById("ingredientMeasurement"+i)}"
        ]`
        if(i < ingredientCount)
        {
            recipeFileContents = recipeFileContents + 
            `,
            `;
        }
    }

    recipeFileContents += 
    `   ],
        "steps": [
            `;

    //Add all steps
    for(i = 1; i < stepCount; i++)
    {
        recipeFileContents +=
        `"${document.getElementById("stepInput"+i).innerText}",
        `
    }


    //Add info
    recipeFileContents +=
    `   ],
        "info": [   ${document.getElementById("prep-time-hr").value}, 
                    ${document.getElementById("prep-time-min").value}, 
                    ${document.getElementById("servings").value}, 
                    ${document.getElemenyById("serving-size").value}, 
                    "${document.getElementById("prep-time-hr").value}" ]`;

    


    // End of JSON contents.  Put a fork in it, it's done!
    recipeFileContents +=
    `   ]
    }   
    `

    //FIXME: This is where I need to write recipeFileContents to test.json

}

I tried using

const fs = require('fs');

        fs.writeFile(filepath, recipeFileContents, (err) => {
            if(err) throw err;
        })

but it said "require is not defined" in the console.