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Creating a NodeJS app with Express 🗂️

Dec 12, 202412 min read

  1. Open an empty directoy
  2. Open a terminal and run npm init -y. This will generate a package.json
  3. Install express: npm install express --safe. This will generate a package-lock.json and a folder called node-modules
  4. Create an index.js
const express = require("express"); //load express library
 
const app = express(); //express app initializing
  1. Create a hello world program:
const express = require("express"); //load express library
 
const app = express(); //express app initializing
 
  
 
//petition get to the root directory, 2nd param is callback function
 
app.get("/", (reequest, response) => {
 
//we have to set what we're going to do with response and request
 
return response.send("Hello world!"); //prints hello world
 
});
 
  
 
//Port listening the inbound traffic
 
app.listen(3000, () => {
 
console.log("App running on http://localhost:3000");
 
});
  1. Create a new folder called store (for databases)
  2. Continue developing the app to read data from a json file:
const express = require("express"); //load express library
 
const fs = require("fs"); //library fileSystem for access information stored
 
const app = express(); //express app initializing
 
  
 
//petition get to the root directory, 2nd param is callback function
 
app.get("/", (request, response) => {
 
//we have to set what we're going to do with response and request
 
return response.send("Hello world!"); //prints hello world
 
});
 
  
 
//Create an endpoint
 
app.get("/todos", (request, response) => {
 
//To read the file we stored on store directory with utf-8 encoding
 
//Last parameter is the callback function
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
  
 
//We are parsing data to JSON because data is actually a string
 
const todos = JSON.parse(data);
 
return response.json({ todos: todos }); //we return a list like the todos.json
 
});
 
});
 
  
 
//Port listening the inbound traffic
 
app.listen(3000, () => {
 
console.log("App running on http://localhost:3000");
 
});

Now check the localhost:3000/todos url 8. Download Postman 9. Create a get petition to the localhost:3000/todos url 10. Remember that express treats const as strings always. Types are very important so make sure your types are correct. 11. Add modify functionality:

const express = require("express"); //load express library
 
const fs = require("fs"); //library fileSystem for access information stored
 
const app = express(); //express app initializing
 
  
 
//petition get to the root directory, 2nd param is callback function
 
app.get("/", (request, response) => {
 
//we have to set what we're going to do with response and request
 
return response.send("Hello world!"); //prints hello world
 
});
 
  
 
//Create an endpoint
 
app.get("/todos", (request, response) => {
 
//To read the file we stored on store directory with utf-8 encoding
 
//Last parameter is the callback function
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
  
 
//We are parsing data to JSON because data is actually a string
 
const todos = JSON.parse(data);
 
return response.json({ todos: todos }); //we return a list like the todos.json
 
});
 
});
 
  
 
//To complete todos on the list
 
app.put("/todos/:id/complete", (request, response) => {
 
const id = request.params.id; //The id of the todo
 
//function that finds a todo by its id
 
const findTodoById = (todos, id) => {
 
//go through the items of the todos list
 
for (let i = 0; i < todos.length; i++) {
 
if (todos[i].id === parseInt(id)) {
 
//parseInt necessary because express treats const as strings by default
 
//if the element's id coincides
 
return i;
 
}
 
}
 
return -1; //if not found
 
};
 
  
 
//To change the value on the file
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
//We are parsing data to JSON because data is actually a string
 
const todos = JSON.parse(data);
 
const todoIndex = findTodoById(todos, id);
 
  
 
if (todoIndex == -1) {
 
return response.status(404).send("File not found");
 
}
 
return response.json(todos[todoIndex]);
 
});
 
}); //quick request to mark a todo
 
  
 
//Port listening the inbound traffic
 
app.listen(3000, () => {
 
console.log("App running on http://localhost:3000");
 
});
  1. Add save to a file functionality:
const express = require("express"); //load express library
 
const fs = require("fs"); //library fileSystem for access information stored
 
const app = express(); //express app initializing
 
  
 
//petition get to the root directory, 2nd param is callback function
 
app.get("/", (request, response) => {
 
//we have to set what we're going to do with response and request
 
return response.send("Hello world!"); //prints hello world
 
});
 
  
 
//Create an endpoint
 
app.get("/todos", (request, response) => {
 
//To read the file we stored on store directory with utf-8 encoding
 
//Last parameter is the callback function
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
  
 
//We are parsing data to JSON because data is actually a string
 
const todos = JSON.parse(data);
 
return response.json({ todos: todos }); //we return a list like the todos.json
 
});
 
});
 
  
 
//To complete todos on the list
 
app.put("/todos/:id/complete", (request, response) => {
 
const id = request.params.id; //The id of the todo
 
//function that finds a todo by its id
 
const findTodoById = (todos, id) => {
 
//go through the items of the todos list
 
for (let i = 0; i < todos.length; i++) {
 
if (todos[i].id === parseInt(id)) {
 
//parseInt necessary because express treats const as strings by default
 
//if the element's id coincides
 
return i;
 
}
 
}
 
return -1; //if not found
 
};
 
  
 
//To change the value on the file
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
//We are parsing data to JSON because data is actually a string
 
let todos = JSON.parse(data); //let allow to modify the content (different from const)
 
const todoIndex = findTodoById(todos, id);
 
  
 
if (todoIndex == -1) {
 
return response.status(404).send("File not found");
 
}
 
  
 
todos[todoIndex].complete = true; //we put the value as true
 
  
 
//we write changes to the file with todos data being stringify (converted back to)
 
fs.writeFile("./store/todos.json", JSON.stringify(todos), () => {
 
return response.json({ status: "ok" });
 
});
 
});
 
}); //quick request to mark a todo
 
  
 
//Port listening the inbound traffic
 
app.listen(3000, () => {
 
console.log("App running on http://localhost:3000");
 
});
  1. Now we apply a filter:
const express = require("express"); //load express library
 
const fs = require("fs"); //library fileSystem for access information stored
 
const app = express(); //express app initializing
 
  
 
//petition get to the root directory, 2nd param is callback function
 
app.get("/", (request, response) => {
 
//we have to set what we're going to do with response and request
 
return response.send("Hello world!"); //prints hello world
 
});
 
  
 
//Create an endpoint
 
app.get("/todos", (request, response) => {
 
//filter all the complete todos ones
 
const showPending = request.query.showpending;
 
//To read the file we stored on store directory with utf-8 encoding
 
//Last parameter is the callback function
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
  
 
//We are parsing data to JSON because data is actually a string
 
const todos = JSON.parse(data);
 
  
 
//if the query paramenter showpending is not equals to the string "1"
 
if (showPending !== "1") {
 
return response.json({ todos: todos }); //we return a list like the todos.json
 
} else {
 
//filter them (return only those which are not completed)
 
return response.json({
 
todos: todos.filter((t) => {
 
return t.complete === false;
 
}),
 
});
 
}
 
});
 
});
 
  
 
//To complete todos on the list
 
app.put("/todos/:id/complete", (request, response) => {
 
const id = request.params.id; //The id of the todo
 
//function that finds a todo by its id
 
const findTodoById = (todos, id) => {
 
//go through the items of the todos list
 
for (let i = 0; i < todos.length; i++) {
 
if (todos[i].id === parseInt(id)) {
 
//parseInt necessary because express treats const as strings by default
 
//if the element's id coincides
 
return i;
 
}
 
}
 
return -1; //if not found
 
};
 
  
 
//To change the value on the file
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
//We are parsing data to JSON because data is actually a string
 
let todos = JSON.parse(data); //let allow to modify the content (different from const)
 
const todoIndex = findTodoById(todos, id);
 
  
 
if (todoIndex == -1) {
 
return response.status(404).send("File not found");
 
}
 
  
 
todos[todoIndex].complete = true; //we put the value as true
 
  
 
//we write changes to the file with todos data being stringify (converted back to)
 
fs.writeFile("./store/todos.json", JSON.stringify(todos), () => {
 
return response.json({ status: "ok" }); //we return ok as it has been modified
 
});
 
});
 
}); //quick request to mark a todo
 
  
 
//Port listening the inbound traffic
 
app.listen(3000, () => {
 
console.log("App running on http://localhost:3000");
 
});
  1. To add items via post requests:
const express = require("express"); //load express library
 
const fs = require("fs"); //library fileSystem for access information stored
 
const app = express(); //express app initializing
 
  
 
//for adding items with post requests
 
app.use(express.json());
 
app.use(express.urlencoded({ extended: true }));
 
  
 
//petition get to the root directory, 2nd param is callback function
 
app.get("/", (request, response) => {
 
//we have to set what we're going to do with response and request
 
return response.send("Hello world!"); //prints hello world
 
});
 
  
 
//Create an endpoint
 
app.get("/todos", (request, response) => {
 
//filter all the complete todos ones
 
const showPending = request.query.showpending;
 
//To read the file we stored on store directory with utf-8 encoding
 
//Last parameter is the callback function
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
  
 
//We are parsing data to JSON because data is actually a string
 
const todos = JSON.parse(data);
 
  
 
//if the query paramenter showpending is not equals to the string "1"
 
if (showPending !== "1") {
 
return response.json({ todos: todos }); //we return a list like the todos.json
 
} else {
 
//filter them (return only those which are not completed)
 
return response.json({
 
todos: todos.filter((t) => {
 
return t.complete === false;
 
}),
 
});
 
}
 
});
 
});
 
  
 
//To complete todos on the list
 
app.put("/todos/:id/complete", (request, response) => {
 
const id = request.params.id; //The id of the todo
 
//function that finds a todo by its id
 
const findTodoById = (todos, id) => {
 
//go through the items of the todos list
 
for (let i = 0; i < todos.length; i++) {
 
if (todos[i].id === parseInt(id)) {
 
//parseInt necessary because express treats const as strings by default
 
//if the element's id coincides
 
return i;
 
}
 
}
 
return -1; //if not found
 
};
 
  
 
//To change the value on the file
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
//We are parsing data to JSON because data is actually a string
 
let todos = JSON.parse(data); //let allow to modify the content (different from const)
 
const todoIndex = findTodoById(todos, id);
 
  
 
if (todoIndex == -1) {
 
return response.status(404).send("File not found");
 
}
 
  
 
todos[todoIndex].complete = true; //we put the value as true
 
  
 
//we write changes to the file with todos data being stringify (converted back to)
 
fs.writeFile("./store/todos.json", JSON.stringify(todos), () => {
 
return response.json({ status: "ok" }); //we return ok as it has been modified
 
});
 
});
 
}); //quick request to mark a todo
 
  
 
//add items with post requests
 
app.post("/todo", (request, response) => {
 
if (!request.body.name) {
 
return response.status(400).send("Missing name");
 
}
 
fs.readFile("./store/todos.json", "utf-8", (err, data) => {
 
//Handling errors
 
if (err) {
 
return response.status(500).send("Something went wrong :("); //http code 500 (error) with a special message
 
} //the next code will not execute
 
  
 
const todos = JSON.parse(data);
 
//We find the max id on the file
 
const maxId = Math.max.apply(
 
Math,
 
todos.map((t) => {
 
return t.id;
 
})
 
);
 
  
 
//We add a new value with a new id higher that higher obtained
 
todos.push({
 
id: maxId + 1,
 
complete: false,
 
name: request.body.name,
 
});
 
  
 
//Write changes to the file
 
fs.writeFile("./store/todos.json", JSON.stringify(todos), () => {
 
return response.json({ status: "ok" }); //we return ok as it has been modified
 
});
 
});
 
});
 
  
 
//Port listening the inbound traffic
 
app.listen(3000, () => {
 
console.log("App running on http://localhost:3000");
 
});
  1. To dockerize the app:
  • Install Docker
  • Open it (make sure it’s opened before doing anything)
  • Create a new file called Dockerfile, where instructions for docker will be descripted
# linux container
FROM node:12
 
# app directory
 
WORKDIR /app
 
# environment variable
 
ENV NODE_ENV production
 
# copy package logs files into the working directory
 
COPY package*.json ./
 
# docker will make npm install
 
RUN npm install
 
# copy all the sources files (from current paste into working directory)
 
COPY . .
 
# installs the library pm2
 
RUN npm install -g pm2
 
# expose the port 3000
 
EXPOSE 3000
 
# executes the library
 
CMD ["pm2-runtime", "index.js"]
  1. Create a new file called .dockerignore and type this to ignore all the node packages:
node_modules
  1. Go to the aws console an type (create a Elastic Container Repository):
    1. ecr >> repositories
    2. Create a new repository
    3. View push commands (execute them)
    4. Type ecs >> clusters (To create a Elastic Cluster) (make sure you use the old version)
    5. Do not click VPC
  2. Go to the tasks definitions of the new cluster:
    1. Create a new one with fargate
    2. Assign a name like taskdef-xxx
    3. Add a task size of 0.5 Gb and 0.25vCPU
    4. Click add container
    5. Put a name (maybe the same as the container you created before) like container-xxx
    6. On image copy the url of the repository where all was store (ecr)
      1. Go back to ecr
      2. Copy the image uri of your latest repository
      4. Keep default soft Limit (128)
      5. Put port 3000 on port maps with protocol tcp
      6. Leave blank the rest and create
  3. Go to the cluster you created before >> Services:
    1. Create a new Service
    2. Select FARGATE
    3. select the latest task definition
    4. Add a task and a service name
    5. Leave the rest by default and click next
    6. Select the VPC of the cluster you want
    7. Add your subnets
    8. Edit security groups
      1. Select Custom TCP
      2. Put the port 3000
      3. Save
    9. Select Application Load Balancer
    10. Put health check period to 30
    11. Create an application load balancer
      1. Select the http/https one
      2. Give it a name like alb-xxx
      3. Listener set to HTTP on port 80 (Create a target group if not exists)
      4. Select the default vpc and select all the subnets
  4. Refresh the tasks view (1~2mis)

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