4.1 Expressions

An expression is a "phrase" of JavaScript that a JavaScript interpreter can evaluate to produce a value. Simple expressions are constants (e.g., string or numeric literals) or variable names, like these:

1.7                               // a numeric literal
"Oh no!  We're out of coffee!"    // a string literal
true                              // a Boolean literal
null                              // the literal null value
i                                 // the variable i
sum                               // the variable sum

The value of a constant expression is simply the constant itself. The value of a variable expression is the value that the variable refers to.

These expressions are not particularly interesting. More complex (and interesting) expressions can be created by combining simple expressions. For example, we saw that 1.7 is an expression and i is an expression, so the following is also an expression:

i + 1.7

(i + 1.7) - sum