Azure Functions simple in-memory CRUD web API

function.json

{
  "bindings": [
    {
      "type": "httpTrigger",
      "direction": "in",
      "webHookTypeX": "genericJson",
      "name": "req",
      "methods": [
        "get",
        "post",
        "put",
        "patch",
        "delete"
      ],
      "authLevel": "anonymous"
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ],
  "disabled": false
}

index.js

var tasks = [
    { text: "watch football", isDone: true },
    { text: "play football", isDone: false },
    { text: "eat crisps", isDone: false },
];

var inMemoryCrud = require('./inMemoryCrud');
inMemoryCrud.seedData(tasks);

module.exports = function (context, req) {
    var requiredFields = ["text", "isDone"];
    inMemoryCrud.handleRequest(context, req, requiredFields);
    context.done();
}

inMemoryCrud.js

var data = [];

var getAll = function() {
    return data;
}

var getById = function(id) {
    return data.find(p => p.id === id );
}

var seedData = function(newItems) {
    newItems.forEach(add);
}

var add = function(newItem) {
    newItem.id = data.reduce((a,b) => a.id > b.id ? a.id : b.id, 0) + 1;
    data.push(newItem);
    return newItem;        
}

var put = function(id, updatedItem) {
    var index = data.findIndex(d => d.id === id);           
    if (index >= 0) {
        updatedItem.id = id;
        data[index] = updatedItem;
        return updatedItem;
    }
    return null;
}

var deleteById = function(id) {
    var index = data.findIndex(d => d.id === id);           
    if (index >= 0) {
        data.splice(index, 1);
        return true;
    }
    return false;
}

var patch = function(id, updatedItem) {
    var item = getById(id);           
    if (item) {
        updatedItem.id = id;
        Object.assign(item, updatedItem);
    }
    return item;
}

var successResponse = function(code, body) {
    return { status: code, body: body };
}

var errorResponse = function(code, message) {
    return { status: code,  body: { error: message } };
}

var handleUpdate = function(req, updateFunc, requiredFields) {
    if (req.query.id) {
        var missingFields = findMissingFields(req.body, requiredFields);
        if (missingFields === "") {
            var id = parseInt(req.query.id);
            var updated = updateFunc(id, req.body);
            if (updated) {
                return successResponse(200, updated);
            }
            return errorResponse(404, 'Item ' + req.query.id + ' not found');
        }
        return errorResponse(400, "Missing required fields: " + missingFields);
    }
    return errorResponse(400, "Please supply item id");
}

var handleDelete = function(req) {
    if (req.query.id) {
        var id = parseInt(req.query.id);
        if (deleteById(id)) {
            return successResponse(200, "deleted");
        }
        return errorResponse(404, 'Item ' + req.query.id + ' not found');
    }
    return errorResponse(400, "Please supply item id");
}


var handleGet = function(req) {
    if (req.query.id) {
        var item = getById(parseInt(req.query.id));
        if (item) {
            return successResponse(200, item);
        }
        return errorResponse(404, 'Item ' + req.query.id + ' not found');
    }
    return successResponse(200, data);
}

var findMissingFields =function(body, requiredFields) {
    return requiredFields.filter(f => !(f in body)).join(',');
} 

var handlePost = function(req, requiredFields) {
    if(typeof req.body === 'object') {
        var missingFields = findMissingFields(req.body, requiredFields);
        if (missingFields === "") {
            var newItem = add(req.body);
            return successResponse(201, newItem);
        }
        return errorResponse(400, "Missing required fields: " + missingFields);
    }
    return errorResponse(400, "must be an object");
}

var handleRequest = function(context, req, requiredFields) {
    if (req.method === 'GET') {
        context.res = handleGet(req);
    }
    else if (req.method === 'POST') {
        context.res = handlePost(req, requiredFields || []);
    }
    else if (req.method === 'PUT') {
        context.res = handleUpdate(req, put, requiredFields || []);
    }   
    else if (req.method === 'PATCH') {
        context.res = handleUpdate(req, patch, []);
    }
    else if (req.method === 'DELETE') {
        context.res = handleDelete(req);
    }
}

module.exports =
    {"handleRequest":handleRequest,
    "seedData": seedData,
    "ver": '0.9' };