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Core JavaScript Guide 1.5 |
Chapter 3 Expressions and Operators
This chapter describes JavaScript expressions and operators, including assignment, comparison, arithmetic, bitwise, logical, string, and special operators.
This chapter contains the following sections:
Expressions
An expression is any valid set of literals, variables, operators, and expressions that evaluates to a single value; the value can be a number, a string, or a logical value.
Conceptually, there are two types of expressions: those that assign a value to a variable, and those that simply have a value. For example, the expression x = 7 is an expression that assigns x the value seven. This expression itself evaluates to seven. Such expressions use assignment operators. On the other hand, the expression 3 + 4 simply evaluates to seven; it does not perform an assignment. The operators used in such expressions are referred to simply as operators.
JavaScript has the following types of expressions:
Arithmetic: evaluates to a number, for example 3.14159 String: evaluates to a character string, for example, "Fred" or "234" Logical: evaluates to true or false Object: evaluates to an object
Operators
JavaScript has the following types of operators. This section describes the operators and contains information about operator precedence.
Assignment Operators Comparison Operators Arithmetic Operators Bitwise Operators Logical Operators String Operators Special Operators JavaScript has both binary and unary operators. A binary operator requires two operands, one before the operator and one after the operator:
A unary operator requires a single operand, either before or after the operator:
In addition, JavaScript has one ternary operator, the conditional operator. A ternary operator requires three operands.
Assignment Operators
An assignment operator assigns a value to its left operand based on the value of its right operand. The basic assignment operator is equal (=), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x.
The other assignment operators are shorthand for standard operations, as shown in the following table.