JavaScript – Expressions and Operators

An expression is a phrase of JavaScript
that a JavaScript interpreter can evaluate to
produce a value. A constant embedded literally in your program is a very
simple kind of expression. A variable name is also a simple expression
that evaluates to whatever value has been assigned to that variable.
Complex expressions are built from simpler expressions. An array access
expression, for example, consists of one expression that evaluates to an
array followed by an open square bracket, an expression that evaluates
to an integer, and a close square bracket. This new, more complex
expression evaluates to the value stored at the specified index of the
specified array. Similarly, a function invocation expression consists of
one expression that evaluates to a function object and zero or more
additional expressions that are used as the arguments to the
function.

The most common way to build a complex expression out of simpler
expressions is with an operator. An operator
combines the values of its operands (usually two
of them) in some way and evaluates to a new value. The multiplication
operator * is a simple example. The
expression x * y evaluates to the
product of the values of the expressions x and y.
For simplicity, we sometimes say that an operator
returns a value rather than “evaluates to” a
value.

This chapter documents all of JavaScript’s operators, and it also
explains expressions (such as array indexing and function invocation)
that do not use operators. If you already know another programming
language that uses C-style syntax, you’ll find that the syntax of most
of JavaScript’s expressions and operators is already familiar to
you.

Comments are closed.