Chapter 5. Statements

Chapter 4 described expressions as JavaScript phrases. By that analogy, statements are JavaScript sentences or commands. Just as English sentences are terminated and separated from one another with periods, JavaScript statements are terminated with semicolons (§2.6). Expressions are evaluated to produce a value, but statements are executed to make something happen.

One way to “make something happen” is to evaluate an expression that has side effects. Expressions with side effects, such as assignments and function invocations, can stand alone as statements, and when used this way are known as expression statements. A similar category of statements are the declaration statements that declare new variables and define new functions.

JavaScript programs are nothing more than a sequence of statements to execute. By default, the JavaScript interpreter executes these statements one after another in the order they are written. Another way to “make something happen” is to alter this default order of execution, and JavaScript has a number of statements or control structures that do just this:

Conditionals

Statements like if and switch that make the JavaScript interpreter execute or skip other statements depending on the value of an expression

Loops

Statements like while and for that execute other statements repetitively

Jumps

Statements like break, return, and throw that cause the interpreter to jump to another part of the program

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