JavaScript code is typically written in a plain text editor or an integrated development environment (IDE) and saved with a ".js" file extension. A script tag is then added to the HTML file to link the JavaScript code to the web page.
The basic structure of a JavaScript program includes variables, functions, and conditional statements. Variables are used to store data and can be declared using the "let" or "const" keywords. Functions are blocks of code that perform specific tasks and can be called multiple times throughout a program. Conditional statements, such as "if-else" statements, are used to execute different code blocks based on certain conditions.
JavaScript also includes a variety of built-in objects, such as the Math and Date objects, which provide additional functionality. Additionally, libraries and frameworks like jQuery and React can be used to simplify the development process and improve code efficiency.
Overall, understanding JavaScript syntax is essential for developing effective and functional web applications. With its flexibility and versatility, JavaScript remains a popular choice for web developers.
JavaScript syntax is the set of rules, how JavaScript programs are constructed:
JavaScript Values
The JavaScript syntax defines two types of values:
- Fixed values
- Variable values
Variable values are called Variables.
JavaScript Literals
JavaScript, literals are values that are written directly into the code and represent fixed values. There are several types of literals in JavaScript, including string literals, numeric literals, boolean literals, and object literals.
String literals are created by enclosing characters in single or double quotes, and can include any combination of letters, numbers, symbols, and spaces. Numeric literals are simply numbers written in the code, and can be integers or floating-point values. Boolean literals are either true or false.
Object literals are a way to create new objects directly in the code, without the need for a constructor function. Object literals consist of key-value pairs enclosed in curly braces, with a colon separating each key-value pair.
Read More:- JS Statements
Literals are a useful tool in JavaScript programming, as they allow for the direct and efficient assignment of fixed values in the code. By understanding the different types of literals in JavaScript, developers can create more efficient and effective code.
The two most important syntax rules for fixed values are:
1. Numbers are written with or without decimals:
2. Strings are text, written within double or single quotes:
JavaScript Variables
JavaScript variables are used to store data values that can be used and manipulated throughout a program. Variables are declared using the "let" or "const" keywords, followed by the variable name and an optional assignment of an initial value.
The "let" keyword is used to declare variables whose values may change throughout the program, while the "const" keyword is used to declare variables whose values are intended to be constant and cannot be changed.
Variables can store a variety of data types, including strings, numbers, booleans, arrays, and objects. The data type of a variable can be determined using the "typeof" operator.
JavaScript also allows for variable scope, which determines where in the program a variable can be accessed. Variables declared within a function are considered local variables and can only be accessed within that function, while variables declared outside of a function are considered global variables and can be accessed throughout the entire program.
Overall, understanding how to use and manipulate variables is an essential component of JavaScript programming. By effectively utilizing variables, developers can create dynamic and responsive web applications.
In a programming language, variables are used to store data values.
JavaScript uses the keywords var, let and const to declare variables.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:
JavaScript Operators
JavaScript uses arithmetic operators ( + - * / ) to compute values:
JavaScript uses an assignment operator ( = ) to assign values to variables:
JavaScript Expressions
In JavaScript, expressions are combinations of values, variables, and operators that can be evaluated to produce a result. JavaScript supports a wide range of expressions, including arithmetic expressions, logical expressions, and conditional expressions.
Arithmetic expressions use mathematical operators, such as addition, subtraction, multiplication, and division, to perform calculations with numerical values. Logical expressions use logical operators, such as "&&" (AND), "||" (OR), and "!" (NOT), to evaluate Boolean values and produce a logical result.
Conditional expressions, such as the ternary operator (?:), allow for conditional execution of code based on a certain condition. For example, the ternary operator can be used to assign a value to a variable based on whether a condition is true or false.
JavaScript also allows for the use of expression statements, which are expressions that are executed as statements. Expression statements are often used to modify the value of a variable or to call a function.
Overall, understanding how to use expressions in JavaScript is essential for creating effective and efficient code. By using expressions to perform calculations, evaluate conditions, and manipulate values, developers can create dynamic and responsive web applications.
An expression is a combination of values, variables, and operators, which computes to a value.
The computation is called an evaluation.
For example, 5 * 10 evaluates to 50:
JavaScript Literals
JavaScript, literals are values that are written directly into the code and represent fixed values. There are several types of literals in JavaScript, including string literals, numeric literals, boolean literals, and object literals.
String literals are created by enclosing characters in single or double quotes, and can include any combination of letters, numbers, symbols, and spaces. Numeric literals are simply numbers written in the code, and can be integers or floating-point values. Boolean literals are either true or false.
Object literals are a way to create new objects directly in the code, without the need for a constructor function. Object literals consist of key-value pairs enclosed in curly braces, with a colon separating each key-value pair.
Read More:- JS Statements
Literals are a useful tool in JavaScript programming, as they allow for the direct and efficient assignment of fixed values in the code. By understanding the different types of literals in JavaScript, developers can create more efficient and effective code.
The two most important syntax rules for fixed values are:
1. Numbers are written with or without decimals:
2. Strings are text, written within double or single quotes:
JavaScript Variables
JavaScript variables are used to store data values that can be used and manipulated throughout a program. Variables are declared using the "let" or "const" keywords, followed by the variable name and an optional assignment of an initial value.
The "let" keyword is used to declare variables whose values may change throughout the program, while the "const" keyword is used to declare variables whose values are intended to be constant and cannot be changed.
Variables can store a variety of data types, including strings, numbers, booleans, arrays, and objects. The data type of a variable can be determined using the "typeof" operator.
JavaScript also allows for variable scope, which determines where in the program a variable can be accessed. Variables declared within a function are considered local variables and can only be accessed within that function, while variables declared outside of a function are considered global variables and can be accessed throughout the entire program.
Overall, understanding how to use and manipulate variables is an essential component of JavaScript programming. By effectively utilizing variables, developers can create dynamic and responsive web applications.
In a programming language, variables are used to store data values.
JavaScript uses the keywords var, let and const to declare variables.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:
JavaScript Operators
JavaScript uses arithmetic operators ( + - * / ) to compute values:
JavaScript uses an assignment operator ( = ) to assign values to variables:
JavaScript Expressions
In JavaScript, expressions are combinations of values, variables, and operators that can be evaluated to produce a result. JavaScript supports a wide range of expressions, including arithmetic expressions, logical expressions, and conditional expressions.
Arithmetic expressions use mathematical operators, such as addition, subtraction, multiplication, and division, to perform calculations with numerical values. Logical expressions use logical operators, such as "&&" (AND), "||" (OR), and "!" (NOT), to evaluate Boolean values and produce a logical result.
Conditional expressions, such as the ternary operator (?:), allow for conditional execution of code based on a certain condition. For example, the ternary operator can be used to assign a value to a variable based on whether a condition is true or false.
JavaScript also allows for the use of expression statements, which are expressions that are executed as statements. Expression statements are often used to modify the value of a variable or to call a function.
Overall, understanding how to use expressions in JavaScript is essential for creating effective and efficient code. By using expressions to perform calculations, evaluate conditions, and manipulate values, developers can create dynamic and responsive web applications.
An expression is a combination of values, variables, and operators, which computes to a value.
The computation is called an evaluation.
For example, 5 * 10 evaluates to 50:
Expressions can also contain variable values:
The values can be of various types, such as numbers and strings.
For example, "John" + " " + "Doe", evaluates to "John Doe":
JavaScript Keywords
JavaScript keywords are reserved words in the language that have a specific meaning and purpose. These keywords cannot be used as variable names or identifiers, as they are already used by the language for specific operations and functions.
Some common JavaScript keywords include "var", "let", and "const", which are used to declare variables. "Function" is used to define a function, while "return" is used to return a value from a function.
"if", "else", and "switch" are used for conditional statements, while "for", "while", and "do-while" are used for looping and iteration. "break" and "continue" are used to control the flow of a loop, while "throw" and "try-catch" are used for error handling.
JavaScript also includes keywords that are used to define classes and objects, such as "class", "constructor", and "this". "import" and "export" are used to include and export modules in a program.
Overall, understanding JavaScript keywords is essential for effective programming in the language. By using the correct keywords for specific operations and functions, developers can create efficient and effective web applications.
JavaScript keywords are used to identify actions to be performed.
The let keyword tells the browser to create variables:
The var keyword also tells the browser to create variables:
JavaScript Comments
Not all JavaScript statements are "executed".
Code after double slashes // or between /* and */ is treated as a comment.
Comments are ignored, and will not be executed:
JavaScript Identifiers / Names
Identifiers are JavaScript names.
Identifiers are used to name variables and keywords, and functions.
The rules for legal names are the same in most programming languages.
A JavaScript name must begin with:
Note: Numbers are not allowed as the first character in names.
The values can be of various types, such as numbers and strings.
For example, "John" + " " + "Doe", evaluates to "John Doe":
JavaScript Keywords
JavaScript keywords are reserved words in the language that have a specific meaning and purpose. These keywords cannot be used as variable names or identifiers, as they are already used by the language for specific operations and functions.
Some common JavaScript keywords include "var", "let", and "const", which are used to declare variables. "Function" is used to define a function, while "return" is used to return a value from a function.
"if", "else", and "switch" are used for conditional statements, while "for", "while", and "do-while" are used for looping and iteration. "break" and "continue" are used to control the flow of a loop, while "throw" and "try-catch" are used for error handling.
JavaScript also includes keywords that are used to define classes and objects, such as "class", "constructor", and "this". "import" and "export" are used to include and export modules in a program.
Overall, understanding JavaScript keywords is essential for effective programming in the language. By using the correct keywords for specific operations and functions, developers can create efficient and effective web applications.
JavaScript keywords are used to identify actions to be performed.
The let keyword tells the browser to create variables:
The var keyword also tells the browser to create variables:
JavaScript Comments
Not all JavaScript statements are "executed".
Code after double slashes // or between /* and */ is treated as a comment.
Comments are ignored, and will not be executed:
JavaScript Identifiers / Names
Identifiers are JavaScript names.
Identifiers are used to name variables and keywords, and functions.
The rules for legal names are the same in most programming languages.
A JavaScript name must begin with:
- A letter (A-Z or a-z)
- A dollar sign ($)
- Or an underscore (_)
Note: Numbers are not allowed as the first character in names.
This way JavaScript can easily distinguish identifiers from numbers.
JavaScript is Case Sensitive
All JavaScript identifiers are case sensitive.
The variables lastName and lastname, are two different variables:
JavaScript does not interpret LET or Let as the keyword let.
JavaScript and Camel Case
Historically, programmers have used different ways of joining multiple words into one variable name:
Hyphens:
first-name, last-name, master-card, inter-city.
Hyphens are not allowed in JavaScript. They are reserved for subtractions.
Underscore:
first_name, last_name, master_card, inter_city.
Upper Camel Case (Pascal Case):
FirstName, LastName, MasterCard, InterCity.
Lower Camel Case:
JavaScript programmers tend to use camel case that starts with a lowercase letter:
JavaScript is Case Sensitive
All JavaScript identifiers are case sensitive.
The variables lastName and lastname, are two different variables:
JavaScript does not interpret LET or Let as the keyword let.
JavaScript and Camel Case
Historically, programmers have used different ways of joining multiple words into one variable name:
Hyphens:
first-name, last-name, master-card, inter-city.
Hyphens are not allowed in JavaScript. They are reserved for subtractions.
Underscore:
first_name, last_name, master_card, inter_city.
Upper Camel Case (Pascal Case):
FirstName, LastName, MasterCard, InterCity.
Lower Camel Case:
JavaScript programmers tend to use camel case that starts with a lowercase letter:
firstName, lastName, masterCard, interCity.
JavaScript Character Set
JavaScript uses the Unicode character set.
Unicode covers (almost) all the characters, punctuations, and symbols in the world.
JavaScript Character Set
JavaScript uses the Unicode character set.
Unicode covers (almost) all the characters, punctuations, and symbols in the world.
