Boolean operator

Boolean operators are used to test the relationship between two values , There are three Boolean operators , Logic is not （！）、 Logic and （&&）, Logic or （||）.

Logic does not consist of an exclamation mark （！） form , It can be applied to JavaScript Any value . Logical non first converts its operands to a Boolean value , And then reverse the Boolean .

console.log(!NaN);//true
console.log(!123);//false
console.log(!"");//true
console.log("");//false
console.log(!{});//false

Logical and are represented by two sums （&&）, There are two operations to do . As shown in the figure below ：var result=true&&false;

 The first operand The second operand result True True True True False False False True False False False False

It can be seen from the above table that only when the first parameter and the second parameter are both true, The result of logic and is true

Logic may consist of two vertical symbols （||）, There are two operands , As shown in the figure below ：var result = true||false;

 The first operand The second operand result True True True True False True False True True False False False

It can be seen from the above table that , The result of one of the operands is true, The result of logical or is true. Both operands are false, The result is false

The multiplication operator consists of an asterisk （*） form , Used to calculate the product of two values .

var num =2*3;
console.log(num);// Output 6

The division operator consists of a slash （/） form , For the calculation of dividing the first operand by the first one .

var num=4/2;
console.log(num);// Output 2

The modulus operator consists of a percent sign （%） form , It's used to calculate the remainder .

var num=5%2;
console.log(num);// Output 1

The addition operator consists of a plus sign （+） form , Used to sum and splice strings .

var num=5+5;
var num1 = 5+"5";
console.log(num);//
console.log(num1);// First the 5 Convert to string and then splice , Output “55”

The subtraction operator consists of a minus sign （-） form ,var result=2-1.

+、- Special use of ：

1. Both numbers are numerical , Then the numerical calculation of addition and subtraction is carried out directly .

2. If one of the operands is NaN, The result is NaN

3. If Infinity+(-)Infinity, The result is NaN

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