Arithmetic operator
Number operation
subtracting
Division will give you a decimal
Remainder x % 7
Abnormal condition, -1%7 === -1, different from our cognition before, because JS extracts negative sign directly, 1%7 is 1, so plus negative sign, it is -1 namely. It doesn’t exist in mathematics, but you can imagine that minus 1 percent 7 is the same thing as 6 percent 7, and the remainder should be 6.
The exponent x ** 3
X ++ / ++x/x– / –x
A ++ takes the first value of a, plus +a takes the last value of a. (The value of a is 2, but the increment is different.)
var a = 10 b = a++ Copy the codeAnd the answer is b is equal to 10,a ++ is equal to 10,a is equal to 11.
A — take the first value of a, take the last value of a. (Both values of A are 4, but the two decrement results are different.)
Evaluate operator +x
Is evaluated
The negative number operator -x
Unlike evaluation operators, negative operators invert the sign of a value
The string operations
Strings support only addition
The following operations are wrong, but JS still gives “results”.
Comparison operator
>
Is greater than
<
Less than
> =
Greater than or equal to
< =
Less than or equal to
= =
JS Trinity diagram
0 == [], 0 == ‘0’, 0 == ‘\t’, 0 == ‘\t’
Don’t use ==, use === instead. The problem with == is that it’s always smart-aleck (automatic type conversion).
X == y truth table
[] == false but not falsy, [] == false but not {}, [[]] == false.
X === y truth table
There is no mystery. Basic types look at value equality and objects look at address equality.
[]! = = [] {}! = = []
Special case NaN! == NaN
! =
= = =
! = =
Boolean operator
Or and not
| | or
&& and
! non
Short circuit logic
Console. log && console.log(‘hi’) defensive programming in case console does not exist.
A = a | | 100 a guaranteed value, there is a a, does not exist for 100. But there’s a loophole, because all five falsy values can make a false.
To avoid this problem, use the following code:
Binary operators
Or, and, no
|
If both bits are 0, the result is 0, otherwise 1
I don’t get the right result because I didn’t convert to binary
&
If both bits are 1, the result is 1; otherwise, 0
~
Invert a binary bit (0 becomes 1,1 becomes 0)
~3 / / - 4
Copy the codeThe above expression applies binary no to 3 to get -4. This result occurs because when bitwise operations are performed, JavaScript internally converts all operators to 32-bit binary integers.
Three forms of 32-bit integer is 00000000000000000000000000000011, whether the binary operation after 11111111111111111111111111111100. Since the first digit is 1, the number is a negative number. JavaScript internally uses the form of complement to represent negative numbers, which means that you need to subtract 1 from the number, negate it again, and then add a negative sign to get the corresponding decimal value. This number minus 1 equals 11111111111111111111111111111011, get 00000000000000000000000000000100, take again the plus minus sign is – 4. And since it’s a little bit of a hassle to do that, you can just remember that if you add something to its negative value, it’s equal to negative 1.
Exclusive or
^
If the two bits are the same, the result is 0, otherwise, 1
Left moves to the right
The < < and > >
0b0001. Moving to the left will complete it.
The right shift operator for header zeroing
>>>
The only difference between the right shift operator (>>>) and the right shift operator (>>) is that when the binary form of a number moves to the right, the head is filled with zeros regardless of the sign bit. So, the operation always gets a positive value. For positive numbers, the result of this operation is exactly the same as the right-shift operator (>>), except for negative numbers.
4 >>> 1
/ / 2
-4 >>> 1
/ / 2147483646
/ * * for binary form for 11111111111111111111111111111100-4, * take the sign bit moves to the right one, you get 01111111111111111111111111111110 * 2147483646 for the decimal. * /
Copy the codeThis operation actually converts a value to a 32-bit unsigned integer.
The fastest way to see how a negative integer is stored inside a computer is to use this operator.
-1 >>> 0 / / 4294967295
Copy the codeCode above, said – 1 as a 32-bit integer, the storage form of internal use unsigned integer format, value is 4294967295 (namely (2 ^ 32) – 1, equal to 11111111111111111111111111111111).
Some use
Use the and operator to determine odd and even
Even number &1 = 0Odd number &1 = 1
Copy the codeUse ~, > >, < < > > >, | to integer
console.log(~~ 6.83) / / 6
console.log(6.93 >> 0) / / 6
console.log(6.83 << 0) / / 6
console.log(6.83 | 0) / / 6
console.log(6.83 >>> 0) / / 6
Copy the codeuse^Swap the values of A and b
var a = 5
var b = 8
a ^= b // A = a ^ b
b ^= a
a ^= b
console.log(a) / / 8
console.log(b) / / 5
Copy the codeOther operators
Some operators
grammar
Property name = property value// Can only be used on objects
Copy the coderole
Reads the property value of an object
doubt
Why can we have properties that are not objects?
'a-b-c'.split(The '-')
Copy the codeJS has special logic, the dot is not an object, it is wrapped as an object
The number will become the number object
A string becomes a string
Bool becomes Boolean
Example: when the number a uses the dot operator
When toString is called, JS first turns A into an object with a method, encapsulating object A1.
Get the toString that encapsulates object A1.
Kill encapsulation object A1.
Void operator.
grammar
voidExpression or statementCopy the coderole
Evaluate an expression or execute a statement
And void is always undefined
demand
<a href="http://example.com" onclick="f(); return false;" > click < / a >
Return false values organize default actions
<a href="javascript: void(f())">
Use void to show off.
Comma operator
grammar
expression1The expression2. , expression nCopy the coderole
Take the value of expression n as the value of the whole
use
Let a = (1, 2, 3, 4, 5)
So the value of A is going to be 5.
Let f = (x) = (console.log(' square = '), x * x)
Note that parentheses cannot be omitted.
Operator priority
What are the priorities
Different operators
1 + 2 * 3 / / return 7
// Multiply and divide first, then add and subtract
Copy the codeIdentical operator
From left to right a plus b plus c
From right to left a = B = C = D
Priority is what comes first, right
Specific rules
Note: parentheses have the highest priority!