JavaScript Statements

JavaScript statements are composed of:
Values, Operators, Expressions, Keywords, and Comments

let x, y, z;    // Statement 1
x = 3;          // Statement 2
y = 4;          // Statement 3
z = x + y;      // Statement 4
              

This statement tells the browser to write "Hello Dolly." inside an HTML element with id="demo":

document.getElementById("demo").innerHTML = "Hello Dolly.";
              

JavaScript Syntax

JavaScript syntax is the set of rules, how JavaScript programs are constructed:

// How to create variables:
var x;
let y;

// How to use variables:
x = 5;
y = 6;
let z = x + y;
              

JavaScript Values

The JavaScript syntax defines two types of values:
Fixed values Variable values Fixed values are called Literals.
Variable values are called Variables.
JavaScript Literals The two most important syntax rules for fixed values are:
1. Numbers are written with or without decimals:

10.50

1001
            

2. Strings are text, written within double or single quotes:

"John Doe"

'John Doe'
            

JavaScript Variables 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.
Example, x is defined as a variable. Then, x is assigned (given) the value 4:

let x;
x = 4;
            

JavaScript Operators

JavaScript uses arithmetic operators ( + - * / ) to compute values: (3 + 4) * 10 JavaScript uses an assignment operator ( = ) to assign values to variables:

let x, y;
x = 3;
y = 4;
            

JavaScript Expressions 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:

5 * 10
//Expressions can also contain variable values:

x * 10
///The values can be of various types, such as numbers and strings.

For example, "John" + " " + "Doe", evaluates to "John Doe":

"John" + " " + "Doe"
            

JavaScript Keywords

JavaScript keywords are used to identify actions to be performed.
The let keyword tells the browser to create variables:

let x, y;
x = 5 + 6;
y = x * 10;
//The var keyword also tells the browser to create variables:

var x, y;
x = 5 + 6;
y = x * 10;
//using var or let will produce the same result.
            

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:

let x = 5;   // I will be executed

// x = 6;   I will NOT be executed
            

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