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JavaScript operator precedence
JavaScript operator precedence, it is describing a sequential operation executed in the calculation expression of computing. Performing first operations with a higher priority, then the execution of low priority operations. For example, we often say that multiplication is performed before addition and then perform addition and subtraction.
Operators JavaScript
| priority | Operators | Explanation | Associativity |
|---|---|---|---|
| 1 | []、.、() |
Field access, array indexing, function calls, and expression grouping | From left to right |
| 2 | ++ -- -~!delete new typeof void | Unary operators, return data type, object creation, undefined value defined |
From right to left |
| 3 | *、/、% | Multiplying, dividing, seeking remainder | From left to right |
| 4 | +、- | Addition, subtraction, string concatenation | From left to right |
| 5 | <<、>>、>>> | Left shift, right shift, unsigned right shift | From left to right |
| 6 | <、<=、>、>=、instanceof | Less than, less than, or equal to, greater than, greater than, or equal to, if an instance of a particular class |
From left to right |
| 7 | ==、!=、===、!== | Equal, not equal, congruent, congruent | From left to right |
| 8 | & | Bitwise "and" | From left to right |
| 9 | ^ | Bitwise "exclusive or" | From left to right |
| 10 | | | Bitwise "or" | From left to right |
| 11 | && | And short-circuit (logical "and") | From left to right |
| 12 | || | Short or (logical "or") | From left to right |
| 13 | ?: | Conditional operator | From right to left |
| 14 | =、+=、-=、*=、/=、%=、&=、|=、^=、<、<=、>、>=、>>= | Mixing assignment operator | From right to left |
| 15 | , | Multiple computing | By priority calculated, and then from right to left |
Javascript parentheses processing operation described
Parentheses are used to change the calculation order determined by the operator precedence. That is, the first calculation expression in parentheses finished, then the value for the rest of the expression.
was Result = 10 * 5 + 3;
document.write(result);
document.write("<br/>");
result = 10 * (5 + 3);
document.write(result);
// output is as follows:
// 53
// 80
In the first expression, in accordance with the priority of operation, the first operation is 10 * 5, then add 3the result to 50.
In the second expression, we are open to change priorities in parentheses, let (5 + 3)the result is 8, then 8go multiplied 10, the result is80
/: Division, such as:int a = 8/9;
%: Modulo arithmetic: int a = 10%2;
Logical operators Javascript
Javascript major distinction == and === , empathy != and !== relationship
There are a = '100'; There are b = 100; document.write(a==b); document.write(a===b); document.write(a!=b); document.write(a!==b); // output is as follows: // true // false // false // true
Since Javascript is a weakly typed language, treatment is not so strict on the type of data, also resulted in the '100'==100;返回true need to compare a little tight '100'===100this time not only comparative value, but also the type of comparison, is returned false.
Similarly != , and !== is the same, the comparison is the value of the former, the latter is the type and value to be compared.
Javascript Operator summary
In fact, in the course of operation, and other languages, it is best to bring direct parentheses, such as var a = 1; a = (a + 100) >>(a+1); and var a = 1; a = a + 100>>a+1;the result is 25, the order of operations is the same, right in front of the more readable?