What is Declaration, Expression, and Statement

Declaration simply means initialization without value.

for example:

let x;

Expression is the operation being used to some primitive data types and will return a value result, like:

• Numerical expression (10+30) 

• String expression ("Hello" + "World!")
• Boolean expression (a > b)
• Conditional expression (age > 18 ? "allow":"exit")

while Statement is just a fancy word to combine both, like:

let x = "Hello" + "World!" // this whole line is called statement