Daisy Rees

Daisy Rees

1560866670

Understanding static in JavaScript

Static properties are properties of a class, not of an instance of a class.

In university, I was taught object-oriented programming in Java. Like most beginners, the first thing I learned was some version of this:

public class HelloWorld {
  public static void main(String[] args) {
    System.out.println("Hello, World");
  }
}

A “Hello, World” program written in Java.

Getting started, I was confused by all these keywords. public, static, void, String, etc… What are all these things!?

Eventually, I learned the meaning behind most of these keywords and how to use them through passive exposure. public makes a class or method available to be used by other programs, void is a type of none, String is an array of chars. These all came naturally as I wrote more Java code. However, static remained a mystery to me for years to come. It simply didn’t come up that often in assignments and projects (except for in that boilerplate main Java method shown above) so there was never a real need to learn its meaning.

When I started learning React a couple years ago I started seeing static and began interacting with it more actively. Here’s an example:

import React from 'react';

class Hello extends React.Component {
  static defaultProps = {
    name: 'World'
  }

  render() {
    return <h1>Hello, {this.props.name}</h1>;
  }
}

Example of static properties in a React component.

Over time, static subconsciously worked it’s way into my development vocabulary, but I still didn’t know why I was using it. I would use it with defaultProps, propTypes, contextTypes, and displayName, and I just assumed it needed to be there for some syntactic reason. I was following patterns that I saw on StackOverflow, and in docs without stopping to think about what static means.

Then I saw a neat example defining state without a constructor:

import React from 'react';

class Counter extends React.Component {
  static displayName = 'Counter';

  state = { count: 0 };

  render() {
    return <h1>{this.state.count}</h1>;
  }
}

A React component with state and no constructor.

In previous examples I’d seen, state was always defined in the constructor of a class, so it caught my interest when I realized state could be defined without a constructor. I also noticed that state isn’t preceded by static which prompted the question: What the heck does static actually do?

And after a quick Google search, I had my answer…

Static properties are properties of a class, not of an instance of a class.
Let’s break that down a bit with an example.

If we have two instances of a React component Foo, the displayName, propTypes, defaultProps will remain the same across both instances, but the state of each instance will be able to update independently of one another.

import React, { Component } from 'react';
import PropTypes from 'prop-types';

class Foo extends Component {
  // attached to the class definition (or prototype)
  static displayName = 'Foo';
  static propTypes = { bar: PropTypes.string };
  static defaultProps = { bar: 'Bar' };
  
  // attached to each new instance of the class/prototype
  state = { hello: 'Hello' };
  
  render() {
    return this.state.hello + this.props.bar;
  }
}

thisFoo will have a state and thatFoo will have a state, but both share the same static properties — displayName, propTypes, and defaultProps— from the class definition.

A Deeper Understanding

This story just scratches the surface of how static is implemented in JavaScript. In reality, the entire class syntax in JavaScript is an abstraction of prototypes.

#javascript #reactjs

What is GEEK

Buddha Community

Understanding static in JavaScript

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

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

#javascript #javascript code #javascript hello world #what is javascript #who invented javascript

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Tyrique  Littel

Tyrique Littel

1604008800

Static Code Analysis: What It Is? How to Use It?

Static code analysis refers to the technique of approximating the runtime behavior of a program. In other words, it is the process of predicting the output of a program without actually executing it.

Lately, however, the term “Static Code Analysis” is more commonly used to refer to one of the applications of this technique rather than the technique itself — program comprehension — understanding the program and detecting issues in it (anything from syntax errors to type mismatches, performance hogs likely bugs, security loopholes, etc.). This is the usage we’d be referring to throughout this post.

“The refinement of techniques for the prompt discovery of error serves as well as any other as a hallmark of what we mean by science.”

  • J. Robert Oppenheimer

Outline

We cover a lot of ground in this post. The aim is to build an understanding of static code analysis and to equip you with the basic theory, and the right tools so that you can write analyzers on your own.

We start our journey with laying down the essential parts of the pipeline which a compiler follows to understand what a piece of code does. We learn where to tap points in this pipeline to plug in our analyzers and extract meaningful information. In the latter half, we get our feet wet, and write four such static analyzers, completely from scratch, in Python.

Note that although the ideas here are discussed in light of Python, static code analyzers across all programming languages are carved out along similar lines. We chose Python because of the availability of an easy to use ast module, and wide adoption of the language itself.

How does it all work?

Before a computer can finally “understand” and execute a piece of code, it goes through a series of complicated transformations:

static analysis workflow

As you can see in the diagram (go ahead, zoom it!), the static analyzers feed on the output of these stages. To be able to better understand the static analysis techniques, let’s look at each of these steps in some more detail:

Scanning

The first thing that a compiler does when trying to understand a piece of code is to break it down into smaller chunks, also known as tokens. Tokens are akin to what words are in a language.

A token might consist of either a single character, like (, or literals (like integers, strings, e.g., 7Bob, etc.), or reserved keywords of that language (e.g, def in Python). Characters which do not contribute towards the semantics of a program, like trailing whitespace, comments, etc. are often discarded by the scanner.

Python provides the tokenize module in its standard library to let you play around with tokens:

Python

1

import io

2

import tokenize

3

4

code = b"color = input('Enter your favourite color: ')"

5

6

for token in tokenize.tokenize(io.BytesIO(code).readline):

7

    print(token)

Python

1

TokenInfo(type=62 (ENCODING),  string='utf-8')

2

TokenInfo(type=1  (NAME),      string='color')

3

TokenInfo(type=54 (OP),        string='=')

4

TokenInfo(type=1  (NAME),      string='input')

5

TokenInfo(type=54 (OP),        string='(')

6

TokenInfo(type=3  (STRING),    string="'Enter your favourite color: '")

7

TokenInfo(type=54 (OP),        string=')')

8

TokenInfo(type=4  (NEWLINE),   string='')

9

TokenInfo(type=0  (ENDMARKER), string='')

(Note that for the sake of readability, I’ve omitted a few columns from the result above — metadata like starting index, ending index, a copy of the line on which a token occurs, etc.)

#code quality #code review #static analysis #static code analysis #code analysis #static analysis tools #code review tips #static code analyzer #static code analysis tool #static analyzer

Ajay Kapoor

1626321063

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