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4.7.7 Order of Evaluation

4.7.7 Order of Evaluation


Operator precedence and associativity specify the order in which operations are performed in a complex expression, but they do not specify the order in which the subexpressions are evaluated. JavaScript always evaluates expressions in strictly leftto-right order. In the expression w=x+y*z, for example, the subexpression w is evaluated first, followed by x, y, and z. Then the values of y and z are multiplied, added to the value of x, and assigned to the variable or property specified by expression w. Adding parentheses to the expressions can change the relative order of the multiplication, addition, and assignment, but not the left-to-right order of evaluation.

Order of evaluation only makes a difference if any of the expressions being evaluated has side effects that affect the value of another expression. If expression x increments a variable that is used by expression z, then the fact that x is evaluated before z is important.

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