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Precedence

The order in which expressions are evaluated based on their operators is known as precedence. Multiplication and division occur before addition and subtraction, so any operands that are to be multiplied or divided occur before ones that are added and subtracted. Precedence can be reordered by placing expressions within parentheses. The innermost parentheses are evaluated first and work outward. So, if you want two numbers added before multiplication, place them in parentheses. The following two script excerpts show the difference results from different precedence order:

						var alpha = 3 * 4 + 7 //alpha's value is 19 — 12 + 7 
var beta = 3 * (4 + 7) // beta's value is 33 — 3 * 11 

When all of the operators have the same precedence, the evaluations occur from left to right. Table 4.3 is a precedence chart, with the lowest ranks being executed before the higher ones.

Table 4.3. Precedence
Rank Operators
1 . [] ()
2 ++ -- - (negation) ∼ ! delete new typeof void
3 * / %
4 + - (subtraction, addition, or concatenation)
5 << >> >>> (bitwise shifts)
6 < > <= >=
7 = = != = = = != =
8 & (bitwise)


Rank Operators
9 ^ (bitwise)
10 | (bitwise)
11 &&
12 ||
13 ?: (ternary)
14 = All compound assignments (such as +=, /=, and &=)
15 ,


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