In every language, evaluation of an expression is done based on a predefined order of precedence which helps the language engine to determine which part of the expression will be evaluated first, which will second, and so on.
Operator precedence in JavaScript
| Operator | Operation | Order of Precedence | Order of Evaluation |
| ++ | Increment | 1 | R -> L |
| — | Decrement | 1 | R -> L |
| — | Negation | 1 | R -> L |
| ! | NOT | 1 | R -> L |
| *, /, | Multiplication, division, modulus | 2 | L -> R |
| +, — | Addition, subtraction | 3 | L -> R |
| + | Concatenation | 3 | L -> R |
| <, <= | Less than, less than, or equal | 4 | L -> R |
| >, >= | Greater than, greater than, or equal | 4 | L -> R |
| == | Equal | 5 | L -> R |
| != | Not equal | 5 | L -> R |
| === | Identity | 5 | L -> R |
| !== | Non-identity | 5 | L -> R |
| && | AND | 6 | L -> R |
| || | OR | 6 | L -> R |
| ?: | Ternary | 7 | R -> L |
| = | Assignment | 8 | R -> L |
| +=, -=, and so on. | Arithmetic assignment | 8 | R -> L |