Dylan  Iqbal

Dylan Iqbal

1548042290

What is this Javascript “require”?

I'm trying to get Javascript to read/write to a PostgreSQL database. I found this project on github. I was able to get the following sample code to run in node.

var pg = require('pg'); //native libpq bindings = `var pg = require('pg').native`
var conString = "tcp://postgres:1234@localhost/postgres";

var client = new pg.Client(conString);
client.connect();

//queries are queued and executed one after another once the connection becomes available
client.query(“CREATE TEMP TABLE beatles(name varchar(10), height integer, birthday timestamptz)”);
client.query(“INSERT INTO beatles(name, height, birthday) values($1, $2, $3)”, [‘Ringo’, 67, new Date(1945, 11, 2)]);
client.query(“INSERT INTO beatles(name, height, birthday) values($1, $2, $3)”, [‘John’, 68, new Date(1944, 10, 13)]);

//queries can be executed either via text/parameter values passed as individual arguments
//or by passing an options object containing text, (optional) parameter values, and (optional) query name
client.query({
name: ‘insert beatle’,
text: “INSERT INTO beatles(name, height, birthday) values($1, $2, $3)”,
values: [‘George’, 70, new Date(1946, 02, 14)]
});

//subsequent queries with the same name will be executed without re-parsing the query plan by postgres
client.query({
name: ‘insert beatle’,
values: [‘Paul’, 63, new Date(1945, 04, 03)]
});
var query = client.query(“SELECT * FROM beatles WHERE name = $1”, [‘John’]);

//can stream row results back 1 at a time
query.on(‘row’, function(row) {
console.log(row);
console.log(“Beatle name: %s”, row.name); //Beatle name: John
console.log(“Beatle birth year: %d”, row.birthday.getYear()); //dates are returned as javascript dates
console.log(“Beatle height: %d’ %d”", Math.floor(row.height/12), row.height%12); //integers are returned as javascript ints
});

//fired after last row is emitted
query.on(‘end’, function() {
client.end();
});

Next I tried to make it run on a webpage, but nothing seemed to happen. I checked on the Javascript console and it just says “require not defined.”

So what is this “require?” Why does it work in node but not in a webpage?

Also, before I got it to work in node, I had to do npm install pg. What’s that about? I looked in the directory and didn’t find a file pg. Where did it put it, and how does Javascript find it?

#javascript #database #postgresql #node.js

What is GEEK

Buddha Community

So what is this “require?”
require() is not part of the standard JavaScript API. But in Node.js, it’s a built-in function with a special purpose: to load modules.

Modules are a way to split an application into separate files instead of having all of your application in one file. This concept is also present in other languages with minor differences in syntax and behavior, like C’s include, PHP’s use, Python’s import, and so on.

One big difference between Node.js modules and browser JavaScript is how one script’s code is accessed from another script’s code.

  • In browser JavaScript, scripts are added via the 

Callum Slater

1548044718

It’s used to load modules. Let’s use a simple example.

In file circle_object.js:

var Circle = function (radius) {
    this.radius = radius
}
Circle.PI = 3.14

Circle.prototype = {
    area: function () {
        return Circle.PI * this.radius * this.radius;
    }
}

We can use this via require, like:

node> require('circle_object')
{}
node> Circle
{ [Function] PI: 3.14 }
node> var c = new Circle(3)
{ radius: 3 }
node> c.area()

The require() method is used to load and cache JavaScript modules. So, if you want to load a local, relative JavaScript module into a Node.js application, you can simply use the require() method.

Example:

var yourModule = require( "your_module_name" ); //.js file extension is optional

Callum Slater

1548045870

Alright, so let’s first start with making the distinction between Javascript in a web browser, and Javascript on a server (CommonJS and Node).

Javascript is a language traditionally confined to a web browser with a limited global context defined mostly by what came to be known as the Document Object Model (DOM) level 0 (the Netscape Navigator Javascript API).

Server-side Javascript eliminates that restriction and allows Javascript to call into various pieces of native code (like the Postgres library) and open sockets.

Now require() is a special function call defined as part of the CommonJS spec. In node, it resolves libraries and modules in the Node search path, now usually defined as node_modules in the same directory (or the directory of the invoked javascript file) or the system-wide search path.

To try to answer the rest of your question, we need to use a proxy between the code running in the the browser and the database server.

Since we are discussing Node and you are already familiar with how to run a query from there, it would make sense to use Node as that proxy.

As a simple example, we’re going to make a URL that returns a few facts about a Beatle, given a name, as JSON.

/* your connection code */

var express = require('express');
var app = express.createServer();
app.get('/beatles/:name', function(req, res) {
    var name = req.params.name || '';
    name = name.replace(/[^a-zA_Z]/, '');
    if (!name.length) {
        res.send({});
    } else {
        var query = client.query('SELECT * FROM BEATLES WHERE name =\''+name+'\' LIMIT 1');
        var data = {};
        query.on('row', function(row) {
            data = row;
            res.send(data);
        });
    };
});
app.listen(80, '127.0.0.1');

Zak Dyer

1548052424

I noticed that whilst the other answers explained what require is and that it is used to load modules in Node they did not give a full reply on how to load node modules when working in the Browser.

It is quite simple to do. Install your module using npm as you describe, and the module itself will be located in a folder usually called node_modules.

Now the simplest way to load it into your app is to reference it from your html with a script tag which points at this directory. i.e if your node_modules directory is in the root of the project at the same level as your index.html you would write this in your index.html:

<script src="node_modules/ng"></script>

That whole script will now be loaded into the page - so you can access its variables and methods directly.

There are other approaches which are more widely used in larger projects, such as a module loader like require.js. Of the two, I have not used Require myself, but I think it is considered by many people the way to go.

Charles Cooper

1548130062

You know how when you are running JavaScript in the browser, you have access to variables like “window” or Math? You do not have to declare these variables, they have been written for you to use whenever you want.

Well, when you are running a file in the Node.js environment, there is a variable that you can use. It is called “module” It is an object. It has a property called “exports.” And it works like this:

In a file that we will name example.js, you write:

example.js

module.exports = "some code";

Now, you want this string “some code” in another file.

We will name the other file otherFile.js

In this file, you write:

otherFile.js

let str = require('example.js')

That require() statement goes to the file that you put inside of it, finds whatever data is stored on the module.exports property. The let str = … part of your code means that whatever that require statement returns is stored to the str variable.

So, in this example, the end-result is that in otherFile.js you now have this:

let string = “some code”;

Note:

the file-name that is written inside of the require statement: If it is a local file, it should be the file-path to example.js. Also, the .js extension is added by default, so I didn’t have to write it.

You do something similar when requiring node.js libraries, such as Express. In the express.js file, there is an object named ‘module’, with a property named ‘exports’.

So, it looks something like along these lines, under the hood (I am somewhat of a beginner so some of these details might not be exact, but it’s to show the concept:

express.js

module.exports = function() {
    //It returns an object with all of the server methods
    return {
        listen: function(port){},
        get: function(route, function(req, res){}){}
     }
}

Rahul Jangid

1622207074

What is JavaScript - Stackfindover - Blog

Who invented JavaScript, how it works, as we have given information about Programming language in our previous article ( What is PHP ), but today we will talk about what is JavaScript, why JavaScript is used The Answers to all such questions and much other information about JavaScript, you are going to get here today. Hope this information will work for you.

Who invented JavaScript?

JavaScript language was invented by Brendan Eich in 1995. JavaScript is inspired by Java Programming Language. The first name of JavaScript was Mocha which was named by Marc Andreessen, Marc Andreessen is the founder of Netscape and in the same year Mocha was renamed LiveScript, and later in December 1995, it was renamed JavaScript which is still in trend.

What is JavaScript?

JavaScript is a client-side scripting language used with HTML (Hypertext Markup Language). JavaScript is an Interpreted / Oriented language called JS in programming language JavaScript code can be run on any normal web browser. To run the code of JavaScript, we have to enable JavaScript of Web Browser. But some web browsers already have JavaScript enabled.

Today almost all websites are using it as web technology, mind is that there is maximum scope in JavaScript in the coming time, so if you want to become a programmer, then you can be very beneficial to learn JavaScript.

JavaScript Hello World Program

In JavaScript, ‘document.write‘ is used to represent a string on a browser.

<script type="text/javascript">
	document.write("Hello World!");
</script>

How to comment JavaScript code?

  • For single line comment in JavaScript we have to use // (double slashes)
  • For multiple line comments we have to use / * – – * /
<script type="text/javascript">

//single line comment

/* document.write("Hello"); */

</script>

Advantages and Disadvantages of JavaScript

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Hire Dedicated JavaScript Developers -Hire JavaScript Developers

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The technology used to develop the overall app by the developers from WebClues Infotech is at par with the latest available technology.

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Niraj Kafle

1589255577

The essential JavaScript concepts that you should understand

As a JavaScript developer of any level, you need to understand its foundational concepts and some of the new ideas that help us developing code. In this article, we are going to review 16 basic concepts. So without further ado, let’s get to it.

#javascript-interview #javascript-development #javascript-fundamental #javascript #javascript-tips

Ajay Kapoor

1626321063

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Santosh J

1622036598

JavaScript compound assignment operators

JavaScript is unarguablly one of the most common things you’ll learn when you start programming for the web. Here’s a small post on JavaScript compound assignment operators and how we use them.

The compound assignment operators consist of a binary operator and the simple assignment operator.

The binary operators, work with two operands. For example a+b where + is the operator and the a, b are operands. Simple assignment operator is used to assign values to a variable(s).

It’s quite common to modify values stored in variables. To make this process a little quicker, we use compound assignment operators.

They are:

  • +=
  • -+
  • *=
  • /=

You can also check my video tutorial compound assignment operators.

Let’s consider an example. Suppose price = 5 and we want to add ten more to it.

var price = 5;
price = price + 10;

We added ten to price. Look at the repetitive price variable. We could easily use a compound += to reduce this. We do this instead.

price += 5;

Awesome. Isn’t it? What’s the value of price now? Practice and comment below. If you don’t know how to practice check these lessons.

Lets bring down the price by 5 again and display it.
We use console.log command to display what is stored in the variable. It is very help for debugging.
Debugging let’s you find errors or bugs in your code. More on this later.

price -= 5;
console.log(price);

Lets multiply price and show it.

price *=5;
console.log(price);

and finally we will divide it.

price /=5;
console.log(price);

If you have any doubts, comment below.

#javascript #javascript compound assignment operators #javascript binary operators #javascript simple assignment operator #doers javascript