Operator precedence determines which operation JavaScript performs first when an expression contains multiple operators. It can interact with automatic type conversion, producing results that differ from the apparent intent. section 3.4.7
Table 3.3. Useful JavaScript operators
|
Operator
|
Description
|
|
++,
--
|
Pre- or post-increment and decrement
|
|
+,
-,
*,
/,
%
|
Addition, subtraction, multiplication, division, remainder
|
|
<,
<=,
>,
>=
|
Less than, less than or equal to, more than, more than or equal to
|
|
==,
!=
|
Equality and inequality tests
|
|
===,
!==
|
Identity and nonidentity tests
|
|
&&,
||
|
Logical AND and OR
|
|
||,
??
|
Null and null-ish coalescing operators
|
|
?
|
Optional chaining operator
|
|
=
|
Assignment
|
|
+
|
String concatenation
|
|
?:
|
Three-operand conditional statement
|
Use the operator table to compare arithmetic, comparison, logical, coalescing, optional chaining, assignment, concatenation, and conditional operators. section 3.4.7
Addition versus concatenation
The expression `5 + 5` produces the number `10`, while `5 + "5"` produces the string `"55"`. String concatenation takes precedence over addition in the relevant mixed-type expression, and JavaScript converts values freely. Convert deliberately when the intended operation matters: `(5).toString() + String(5)` produces a string, whereas `Number("5") + parseInt("5")` produces the number `10`. section 3.4.7
Avoid ambiguous expressions by making both the operation and the expected type explicit.
- Use parentheses before calling a method on a numeric literal, as in `(5).toString()`. section 3.4.7
- Convert strings with `Number` or `parseInt` when arithmetic is intended. section 3.4.7
- Inspect both the value and `typeof` result when an expression may combine operators and types. section 3.4.7
