JS learning notes - operators

Operator ( operator ) Also known as the operator , Is used to implement assignment 、 Symbols that compare and perform functions such as arithmetic operations .

  The precision of floating point numbers

The highest precision of a floating-point value is 17 Decimal place , But the accuracy of arithmetic calculation is far less than integer .

Increment and decrement operators

If you need to add or subtract numbers repeatedly 1 , have access to Increasing ( ++ ) And decline ( -- ) Operator To complete .

stay JavaScript in , Increasing ( ++ ) And decline ( -- ) You can put it in front of a variable , You can also put it after variables . When you put it in front of a variable , We can call it Pre increment ( Decline ) Operator , When you put it after a variable , We can call it Post increment ( Decline ) Operator .

Increment and decrement operators must be used with variables .

Pre increment and post increment operators can simplify the writing of code , Let the value of the variable + 1 Easier to write than before

When used alone , The running results are the same , When used with other code , The execution results will be different .

After : First the original value operation , Post autoplus ( Put the interest of others above one's own )

In front of : Add it first , Post operation ( First, then )

Comparison operator

The equal sign in our program is   ==   Default conversion data type Will convert string data to numeric data

Logical operators

Logical operators are used to Operators that perform Boolean operations , Its return value is also Boolean .

  Logic and && and On both sides true The result is true As long as there is Side is false The results for false

Logic or || or On both sides false It turns out to be false false As long as there is one Side is true junction The result is true

Logic is not (!) It's also called the negation , Used to take a value that is the opposite of a Boolean value , Such as true The opposite of this is false

Short-circuit operation ( Logic break )

Logic and short circuit operation

The principle of short circuit operation : When there are multiple expressions ( value ) when , When the value of the expression on the left can determine the result , The value of the expression on the right will no longer be evaluated ;

Logic and short circuit operation ： If the expression 1 The result is true , Then return the expression 2. If the expression 1 For false , Then the return expression 1

If the empty or negative is false, the rest is true .eg: 0  ' '  null  undefined   NaN

Logic or short circuit operation

Logical or short circuit operation if expression 1 If the result is true, the expression is returned 1 If the expression 1 Returns an expression if the result is false 2

Assignment operator

  Operator priority