5.1 Expression Statements

The simplest kind of statements in JavaScript are expressions that have side effects. We've seen this sort of statement in the section on operators in Chapter 4, Expressions and Operators. One major category of these are assignment statements. For example:

s = "Hello " + name;
i *= 3;

Related to assignment statements are the increment and decrement operators, ++ and --. These have the side effect of changing a variable value, just as if an assignment had been performed:

counter++;

Function calls are another major category of expression statements. For example:

alert("Welcome, " + name);
window.close();

These functions calls are expressions, but also produce an effect on the web browser, and so they are also statements. If a function does not have any side effects, then there is no sense in calling it, unless it is part of an assignment statement. So, for example, you wouldn't just compute a cosine and discard the result:

Math.cos(x);

Instead, you'd compute the value and assign it to a variable for future use:

cx = Math.cos(x);