Expression Evaluation in JavaScript
In JavaScript, an expression is any valid set of literals, variables, operators, and expressions that evaluates to a single value. The value can be a number, a string, or a logical value. Conceptually, there are two types of expressions: those that assign a value to a variable, and those that simply have a value.
Let’s look at some examples:
Literals: These are simplest form of JavaScript expressions. When they are evaluated, they produce a value.


Arithmetic Expressions: These are mathematical expressions that use arithmetic operators (like +
, 
, *
, /
, etc.).


Logical Expressions: These use logical operators (&&
, 
, !
) and evaluate to a boolean value.


Expressions with function calls: Functions return a value, so a function call can be an expression too.


Assignment Expressions: An assignment uses the =
operator to assign a value to a variable. This type of expression evaluates to the assigned value.


Expressions with objects and arrays: JavaScript has literals for creating objects and arrays.


Compound Expressions: JavaScript expressions can be part of bigger expressions.


In the last example, x * 10
is an expression (which evaluates to 50), x * 10 + 5
is an expression (which evaluates to 55), and y = x * 10 + 5
is also an expression (which evaluates to 55).
So, as you can see, every expression in JavaScript evaluates to some value. This is a fundamental aspect of how JavaScript, and indeed most programming languages, work.