What Are Expressions and Statements in JavaScript?

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What is an expression in JavaScript?

An expression is a fragment of code that produces a value.

For example, you got literal values like 43 or “happy.” These are always expressions!

Expressions are also considered something in between parentheses.

Binary and unary operators that hold 2 expression values or 1 are also fully considered expressions as well.

This also infers that expressions can contain other expressions, nested within each other.

What is a statement in JavaScript?

If you think about expression as part of a sentence, then a statement would be the entire sentence.

A full program consists of a list of statements in JavaScript.

If you’re having trouble recognizing a statement, you can tell by the semicolon in front of it.

If it’s got a semicolon in front of it, that entire line is a statement.

A statement can stand on its own in JavaScript.

Disclaimer: JavaScript sometimes doesn’t require a semicolon at the end of a statement. However, if it’s not required doesn’t mean you have to omit it. You can still just add in a semicolon just to keep it easy to understand.

How to tell the difference between an expression and a statement

Here’s an example of an expression:

22

22 is a literal number.

"happy"

The word happy is also a literal string.

But if you wanted a statement, it looks something like this:

22;

Notice the semicolon to the right of 22? That’s what makes it a statement.

!true;

!true; is a statement because it’s also got a semicolon to the right of it.

Side effects: When a statement changes what comes after it

When a statement is used to change what comes after it, the concept is called side effects.

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