JavaScript Cheat Sheet: A Complete Guide

Have you ever found yourself stuck on a tricky piece of code or forgotten a crucial syntax? With the JavaScript Cheat Sheet, you’ll have all the key information at your fingertips, making coding smoother and more enjoyable. From fundamental concepts to advanced strategies, this comprehensive blog ensures you have everything you need to write clean, efficient, and effective JavaScript code.

Imagine having a handy reference that covers everything from basic commands to advanced techniques, all in one place. With our JavaScript Cheat Sheet, you’ll be able to code more efficiently, solve problems faster, and enhance your overall productivity. This comprehensive blog is designed to provide easy access to all the essential JavaScript concepts, ensuring you never miss a beat.

Table of Contents

1) Understanding JavaScript Cheat Sheet

2) What Does JavaScript Cheat Sheet Include?

3) JavaScript Engine

4) What is the Difference Between Java and JavaScript?

5) Conclusion

Understanding JavaScript Cheat Sheet

JavaScript Cheat Sheet gives you a concise guide to key JavaScript concepts like syntax, methods, data types, operators, control flow, DOM manipulation, and error handling. The Cheat Sheet is extremely useful for both budding and professional developers. Additionally, understanding JavaScript Operators helps you create an effective user experience too.

The following are some of the integral parts of the JavaScript Cheat Sheet:

1) Basics: Variables, using let and const, are storage units. While the data types, like Number, String, and Object, dictate the kind of data stored.

2) Functions: They're reusable blocks of code. Whether defined traditionally or as modern arrow functions, they're integral for modular coding.

3) Control structures: Directing the flow of code is achieved through conditions like if or switch and loops, such as for or while.

4) Objects and arrays: Both provide structured ways to store data. Objects utilise key-value pairs, and arrays use indexed lists.

5) DOM manipulation: It is the bridge between JavaScript and HTML. It allows dynamic content updates and interactivity.

6) Advanced concepts: Asynchronous operations, leveraging promises and async/await, enable non-blocking code.

7) Best practices: Adopting standards like 'strict mode' ensure code integrity.

8) Common methods: In-built functions like split() or map() facilitate data processing.

9) Debugging: Essential tools like console.log() and breakpoints assist in identifying and resolving issues.

10) External libraries: Libraries like jQuery or React extend JavaScript's capabilities, making tasks more manageable.

What Does JavaScript Cheat Sheet Include?

Before you start learning JavaScript, we are going to provide you with some useful examples so that you can refer to this Sheet to help you along the way.

Let us start by learning: what are the JavaScript Data Types?

There are two data types: Primitive Type and Non-Primitive Type.

Primitive type: It includes Number, BigInt, String, Boolean, Symbol, Undefined and Null.

Non-primitive type: It includes Object, Array, and Functions.

In this Cheat Sheet, we’ll give you a brief overview of both data types and more so that you can use this on the go. Let's begin:

Primitive Type

JavaScript program manipulates values. These values belong to a “type”. These seven primitive data types are:

1) Number: This is used for all kinds of number values, both integer and floating point. However, the very big integers are exempted from this category. This is an IEEE 754 64-bit double-precision floating point value. Within this programming language, it does not differentiate between floating-point numbers and integers.

Example:

let x = 5; //An example of a whole number (integer) let y = 3.14; //An example of a decimal number (floating-point) let z = -10; // An example of a negative number   console. log(typeof x); // Output: “number” console. log(typeof y); // Output: “number” console. log(typeof z); // Output: “number”

In this above example, we created two symbols using the ‘Symbol()’ function. The first symbol,’symbol1’, has no description associated with it. The second symbol,’ symbol2’, has a description provided as a string parameter to the ‘Symbol()’ function.

Symbols are unique, even if they have the same description.

2) BigInt: This is used arbitrarily for all kinds of large integers. This means that it allows you to work with numbers which are larger than the maximum value that can be represented by the ‘number’ type.

Example:

let bigNumber = 1234567890123456789012345678901234567890n; let anotherBigNumber = BigInt (987654321098765432109876543210n”);   console.log(typeof bigNumber); // Output: “bigint” console.log(typeof anotherBigNumber); // Output: “bigint” console.log(bigNumber); // Output: 1234567890123456789012345678901234567890n console.log(anotherBigNumber); // Output: 987654321098765432109876543210n

In this above example, we see an additional operation between ‘bigNumber’ and ‘100n’. The result is ‘bigint’ and a regular ‘number’ (like un ‘mixedResult’), an error will occur. To mix ‘bigint’ and ‘number’ types, you would need to convert one of them to match the other.

Keep following this JavaScript Cheat Sheet to know more!

3) Boolean: Now, we’ll introduce you to another primitive type of JavaScript in this Cheat Sheet – called Boolean. This type is used to represent logical values, either ‘true’ or ‘false’. Boolean values are also commonly used in conditional statements and logical operations.

Example:

let isTrue = true; let isFalse = false; console.log(typeof isTrue); // Output: “boolean” console.log(typeof isFalse); // Output: “boolean” console.log(isTrue); // Output: true console.log(isFalse); // Output: false

4) Symbol: This type is used to create immutable unique values that can be used as object properties. This type is often used as keys in object properties, which ensures their uniqueness. It also creates private members in classes or defines system-level symbols. Hence, you can use this type for advanced JavaScript scenarios.

Example:

let symbol1 = Symbol(): let symbol2 = Symbol(“description”); console.log(typeof symbol1); // Output: “symbol” console.log(typeof symbol2); // Output: “symbol” console.log(symbol1); // Output: Symbol() console.log(symbol2); // Output: Symbol(description)

In this above example, we created two symbols using the ‘Symbol()’ function. The first symbol,’symbol1’, has no description associated with it. The second symbol,’ symbol2’, has a description provided as a string parameter to the ‘Symbol()’ function.

Symbols are unique, even if they have the same description.

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5) String: This type of JavaScript is used to represent textual data.

For example:

let message = “Hello, World!” let name = ‘John’; console.log(typeof message); // Output: “string” console.log(typeof name); // Output: “string” console.log(message); // Output: “Hello, World!” console.log(name); // Output: “John”

As you can see, in the above example, we had declared two variables, 'message’ and ‘name’, as ‘string’ values. The ‘message’ variable holds the string “Hello, World!”, and the ‘name’ variable holds the string “John”.

In this Sheet, you will come to know that the Strings can be created using single quotes (‘) or double quotes (“). If you use even any one way, both are valid, and you can also use them interchangeably. As per your convenience, choose the style as JavaScript treats them the same.

6) Undefined: This type represents a variable that has been declared, but the value has not yet been assigned. You may also know this type as the default value of uninitialised variables. In other words, it represents the absence of a value or the lack of a defined value.

Let’s take an example:

let undefinedVariable; let nullVariable = null;   console.log(undefinedVariable); // Output: undefined console.log(nullVariable); // Output: null

As you see in the example above, we declared two variables,’undefinedVariable’ and ‘nullVariable’. ‘undefinedVariable’ is declared without assigning a value, while ‘nullVariable’ is explicitly assigned the value ‘null’.

7) Null: Another type in this Cheat Sheet that is often used to indicate that a variable or object property has no value assigned to it. This data type represents the intentional absence of any object value.

For example:

let nullVariable = null;

console.log(nullVariable); // Output: null

In this example above, we have declared a variable called ‘nullVariable’ and assigned its value ‘null’. This shows that the variable intentionally has no value or object associated with it.

But how do you differentiate ‘null’ from ‘undefined’? The answer is simple. ‘undefined’ is used for variables that have been declared but have not been assigned a value. Whereas ‘null’ is that type when you will explicitly indicate the absence of an object or value.

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Non-primitive type:

We have just discussed the seven primitive data types. Now, we will discuss the non-primitive type in this same JavaScript Cheat Sheet. Let’s go!

Data type	Description
1. Object	A collection of key-value pairs
2. Array	An ordered list of values
3. Function	A reusable block of code

To have a reference on these data types, we have listed some examples from each category so that you can practice before you take a deep dive into JavaScript. Let’s have a look!

1) Object: This is a kind of data type which allows the storage and organisation of related data and functionality through key-value pairs.

Example:

let person = {       name: “John”,        age: 30,        isstudent: false,        address: {             street: “123 Main St”,              city: “Exampleville”               country: “Exampleland” }, hobbies: [“reading”, “playing guitar”, “hiking”], sayHello: function() {      console.log(“Hello, I’m “ + this.name); }         }; console.log(person.name); // Output: “John” console.log(person.age); // Output: 30 console.log(person.address.city); // Output: “Exampleville” console.log(person.hobbies[0]); // Output: “reading” person.sayHello(); // Output: “Hello, I’m John”

2) Array: This data type is an ordered collection of elements that can hold multiple values of different types in a single variable, similar to how a JavaScript Array functions.

Example:

let numbers = [1, 2, 3, 4, 5]; let fruits = ["apple", "banana", "orange"]; let mixedArray = [10, "hello", true, { name: "John" }];    console.log(numbers[0]); // Output: 1 console.log(fruits.length); // Output: 3 console.log(mixedArray[2]); // Output: true    numbers.push(6); console.log(numbers); // Output: [1, 2, 3, 4, 5, 6]    fruits[1] = "grape"; console.log(fruits); // Output: ["apple", "grape", "orange"]    let slicedArray = mixedArray.slice(1, 3); console.log(slicedArray); // Output: ["hello", true]

3) Function: This data type is a reusable block of code that can be invoked to perform a specific task or computation

function greet(name) { console.log("Hello, " + name + "!"); }   greet("John"); // Output: "Hello, John!"              greet("Alice"); // Output: "Hello, Alice!"

3) Objects in JavaScript

Objects are among the most versatile types in JavaScript, with nearly “everything” being an object. Standard built-in objects include:

a) Booleans can be objects (when defined with the new keyword)

b) Numbers can be objects (when defined with the new keyword)

c) Strings can be objects (when defined with the new keyword)

d) Dates are always objects

e) Math objects are always objects

f) Regular expressions are always objects

g) Arrays are always objects

h) Functions are always objects

i) Objects are inherently objects

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4) Type Coercion

Type coercion in JavaScript denotes an automatic or implicit conversion of values from one data type to another. This process occurs when different types of values are used together in an operation. Here are the three main types of conversions:

1) To String: Converting a value to a string. For example, when a number is added to a string, the number is coerced to a string:

let result = 5 + "5"; console.log(result); // "55" console.log(typeof result); // "string"

2) To Boolean: Converting a value to a boolean

let result = !!"hello"; console.log(result); // true console.log(typeof result); // "boolean"

3) To Number: Converting a value to a number. For example, when a string is used in a mathematical operation, it is coerced to a number:

let result = "5" * 2; console.log(result); // 10 console.log(typeof result); // "number"

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Operators:

Operators are symbols which are used to perform various operations on variables.

With the help of this concise table, we have given you some examples of Operators:

Operator	Description	Example
Assignment	Assigns a value to a variable	Let x = 5;
Arithmetic	Performs mathematical calculations	Let isTrue = true && false
Comparison	Compares values and returns a Boolean result	Let isGreater = 5 > 3;
Logical	Performs logical operations and returns a Boolean result	Let isTrue = true && false
Unary	Performs operations on a single operand	Let x = 5; X++;
Increment/Decrement	Increases or decreases variable by 1	Let count: 0; Count++;
Conditional (Ternary)	Assigns a value based on a condition	Let fullName = firstName + ‘ ‘ + lastName;

JavaScript Engine

A JavaScript engine is a software component, which executes JavaScript code. Initially, JavaScript engines were simple interpreters, but modern engines use just-in-time (JIT) compilation for improved performance. Here are some of those engines:

1) The Parser

Parsing involves analysing the source code, checking for errors, and breaking it down into components. This process ensures that the code is syntactically correct and ready for further processing.

2) The AST

An Abstract Syntax Tree (AST) is a tree representation of the source code that highlights structural or content-related details without showing every detail of the original syntax. Some elements are implicit in the tree, hence the term “abstract.”

For example, you can consider this JavaScript code:

const sum = (a, b) => a + b;

The corresponding AST might look something like this:

Program └── VariableDeclaration      ├── VariableDeclarator      │   ├── Identifier (sum)      │   └── ArrowFunctionExpression      │       ├── Parameters (a, b)      │       └── BinaryExpression (+)      │           ├── Identifier (a)      │           └── Identifier (b)

3) The Interpreter

An interpreter executes code line by line without needing to compile it into machine language first. To enhance performance, interpreters can parse and execute source code immediately, translate it into more efficient machine code, execute precompiled code from a compiler, or use a combination of these methods.

4) The Compiler

The compiler converts instructions into machine code or a lower-level form ahead of time, allowing the computer to read and execute the code. It processes all the code, determines its functionality, and compiles it into a more readable language for the computer.

5) The Combo

The combo refers to the combination of various techniques and components that work together to execute JavaScript code efficiently. Some of its key elements are compilation, execution, optimisation, and so on. GraphQL Cheat Sheet is one such tool that aids in understanding and optimising these components.

What is the Difference Between Java and Javascript?

To help you not get confused between Java and JavaScript, we have prepared a short table for you to glance through:

Java	JavaScript
Compiled	Interpreted
Used for general purpose	Used for web development
Object-oriented	Supports OOP but is flexible
Extensive standard library	ECMAScript standard library with API
Syntax like C++	Syntax like C
Static checking	Dynamic checking

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Conclusion:

With the help of this Cheat Sheet, you should be able to find all the necessary codes and references on the go. However, it is always advisable to gain detailed knowledge and then use the JavaScript Cheat Sheets to hone your learning. Additionally, exploring jQuery Project Ideas can be a great way to apply your skills practically. This sheet has provided all the essential information required for JavaScript Developers.

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