You can write JavaScript using an object-oriented paradigm, using prototypes and the new as of ES6 classes syntax. You can write JavaScript in a functional programming style, with its first-class functions, or even in an imperative style C-like. A little bit of history Created in , JavaScript has gone a very long way since its humble beginnings. Just JavaScript Sometimes it's hard to separate JavaScript from the features of the environment it is used in.
In this book I talk about JavaScript, the language. A brief intro to the syntax of JavaScript In this little introduction I want to tell you about 5 concepts: white space case sensitivity literals identifiers comments White space JavaScript does not consider white space meaningful. For example, I always use 2 space characters for each indentation. Case sensitive JavaScript is case sensitive. The same goes for any identifier.
Some names are reserved for JavaScript internal use, and we can't use them as identifiers. Comments Comments are one of the most important parts of any program, in any programming language. My personal preference is to avoid semicolons, so my examples in the book will not include them. Values A hello string is a value. Variables A variable is a value assigned to an identifier, so you can reference and use it later in the program. A variable must be declared before you can use it.
We have 2 main ways to declare variables. Using let you can assign a new value to it. Types Variables in JavaScript do not have any type attached. They are untyped. Primitive types Primitive types are numbers strings booleans symbols And two special types: null and undefined.
Object types Any value that's not of a primitive type a string, a number, a boolean, null or undefined is an object. We'll talk more about objects later on. Expressions An expression is a single unit of JavaScript code that the JavaScript engine can evaluate, and return a value. Expressions can vary in complexity.
We start from the very simple ones, called primary expressions: 2 0. Operators Operators allow you to get two simple expressions and combine them to form a more complex expression. What operations are executed first, and which need to wait? You can use the following operators to compare two numbers, or two strings.
Conditionals With the comparison operators in place, we can talk about conditionals. And if you have a single statement to execute after the conditionals, you can omit the block, and just write the statement: if true doSomething But I always like to use curly braces to be more clear. You can provide a second part to the if statement: else. Arrays in JavaScript are not a type on their own.
Arrays are objects. A commonly used syntax is: a. Strings A string is a sequence of characters. It can be also defined as a string literal, which is enclosed in quotes or double quotes: 'A string' "Another string" I personally prefer single quotes all the time, and use double quotes only in HTML to define attributes. Its length property is 0: ''. JavaScript provides many way to iterate through loops. I want to focus on 3 ways: while loops for loops for..
This means the block is always executed at least once. Functions are a core, essential part of JavaScript. What is a function? A function is a block of code, self contained.
You can only return one value. You can return a function from a function, too. Arrow functions Arrow functions are a recent introduction to JavaScript.
Arrow functions are anonymous. We must assign them to a variable. Arrow functions can also contain other arrow functions, or even regular functions.
Objects Any value that's not of a primitive type a string, a number, a boolean, a symbol, null, or undefined is an object. Object Properties Objects have properties , which are composed by a label associated with a value. As you can see, when we have multiple properties, we separate each property with a comma.
We can retrieve the value of a property using 2 different syntaxes. The first is dot notation : car. This is the reason why regular functions are often used as object methods. In this chapter we'll go up one level by introducing classes. What are classes? They are a way to define a common pattern for multiple objects.
We can set the value of the name property: flavio. Classes can hold properties, like name , and methods. Normally methods are defined on the object instance, not on the class. Inheritance A class can extend another class, and objects initialized using that class inherit all the methods of both classes. I am also a programmer. This means that a line of code is executed, then the next one is executed, and so on. Everything is as you expect, and how it works in most programming languages.
However, there are times when you cannot just wait for a line of code to execute. You can't just wait 2 seconds for a big file to load, and halt the program completely.
You can't just wait for a network resource to be downloaded before doing something else. Help to translate the content of this tutorial to your language! How it's done now. From the basics to advanced topics with simple, but detailed explanations. Main course contains 2 parts which cover JavaScript as a programming language and working with a browser. There are also additional series of thematic articles. Learning how to manage the browser page: add elements, manipulate their size and position, dynamically create interfaces and interact with the visitor.
We want to make this open-source project available for people all around the world. Tutorial map. Light theme Dark theme. Last updated at 14th January Table of contents Main course contains 2 parts which cover JavaScript as a programming language and working with a browser. We concentrate on the language itself here, with the minimum of environment-specific notes. An introduction. An Introduction to JavaScript.
Manuals and specifications. JavaScript Fundamentals. The modern mode, "use strict". Interaction: alert, prompt, confirm.
Type Conversions. Conditional branching: if, '? Logical operators. Nullish coalescing operator '?? The "switch" statement.
Function expressions. Arrow functions, the basics. JavaScript specials. Code quality. Debugging in the browser. Automated testing with Mocha. Polyfills and transpilers. Objects: the basics. Object references and copying. They allow you to execute blocks of code desired number of times with different values:.
These types of statements are easy to understand. Using them, you can set conditions for when your code is executed. If certain conditions apply, something is done, if not — something else is executed.
A similar concept to if else is the switch statement. However, using the switch you select one of several code blocks to execute.
Strings are what JavaScript calls to text that does not perform a function but can appear on the screen. In JavaScript, strings are marked with single or double-quotes. If you want to use quotation marks in a string, you need to use special characters:.
Regular expressions are search patterns used to match character combinations in strings. The search pattern can be used for text search and text to replace operations. You can also work with and modify dates and time with JavaScript. This is the next chapter in the JavaScript cheat sheet. It is the code of the structure of a webpage. Besides HTML elements, JavaScript is also able to take into account the user browser and incorporate its properties into the code. Events are things that can happen to HTML elements and are performed by the user.
The programming language can listen for these events and trigger actions in the code. Users may also disable JavaScript in their viewer application.
Digital signatures may also add their own complications to the mess. Worst of all, it is not all that easy to add JavaScript or debug it. Gnostice wishes you good luck in your personal forays into AcroJS.
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