Basics of operators

Operator

Arithmetic operator

When it comes to computation , Space before and after is required , +: There are strings involved , Will become a splice -: Try to turn the data on both sides into numerical values , * , / %: model , Remainder , Big model small , Remainder , Small mold big , Take small , **

 let num = 1 + 2;
      let num1 = "1" + 2
      console.log(num);//3
    console.log(num1);//12

    // 100  Set to style Inside width top left "100px"
    let num3 = 100 + "px"
    console.log(num3);

    let a;
    let num3 = "123" - a
    console.log(num3); //NaN

    let num3 = 100 / 0
    console.log(num3); //Infinity

    let num = 0 / 0
    console.log(num);//NaN

    let num = 6 % 5
    console.log(num); //1

    let num3 = 4 % 9
    console.log(num3); //4

    let num4 = 3 ** 3
    console.log(num4);//27

Assignment operator

 	 let obj = {
    
             name:' Finch ',
             age:3
         	}

       	 let a = obj.age 

         obj.age = 108

         console.log(a);//3


        let obj = {
    
            name:' Finch ',
            age:[1,2]
        }

        let a = obj.age 
        
        obj.age[0] = 2

        console.log(a[0]);//2

In front of ++ And post ++ The difference between

The pre and post values are not assigned , The result is the same ,
When there is an assignment ： In front of ： Evaluate first and then assign , After ： Assign first , In the operation

 let num = 1
        // num = num + 1
        num += 5
        console.log(num); //2

        //  No assignment behavior 
        let num = 9
        ++num
        console.log(num); //10

        //  There is assignment behavior 
        let x = 9
        let num1 = ++x  // The preposition needs to be calculated first , In assignment 
        console.log(num1);//10

        let y = 9
        let num2 = y++ // The postposition needs to be assigned first , Post operation 
        console.log(num2);//9

Comparison operator

It usually appears when judging the conditions , Returns a Boolean value by comparison , If the conditions are met true, If the condition is not met, it is false

=
<
<=
== Judge whether they are equal Do not look at the data type equal true It's not equal false
!=
The above comparison operators If one side is numerical , Will try to turn the other side into a numerical value to compare the size
=== All equal to Strict comparison The type is required to be consistent There is no type conversion
!== It's not equal to Strict comparison

  let bool = 2 > 1
        console.log(bool); //true

        let bool = undefined === undefined
        console.log(bool); //true

        let bool = NaN === NaN 
        console.log(bool); //false

        let bool = [] === []
        console.log(bool);//false

        let arr = []	//[]1 The address of 
        let arr1 = arr 	//[]1 The address of 
        console.log(arr === arr1); //true

        let bool = {
    } === {
    }
        console.log(bool); //false

        let bool = {
    } == {
    }
        console.log(bool); //false  As long as it's a different object   It's not equal 

Logical operators

&& And : encounter true Just through , encounter false Just stop and return the value ,( Too true to leave , Like fake )
|| or : encounter false Just through , encounter true Just stop and return the value ( Leave the real thing after the holiday , Like the real thing )
！ Not : Take the opposite To the opposite Boolean value ！！ Take two reverses , Then it becomes the Boolean value of the transformation corresponding to the value

Priority is not first and then or

        let a = 1 && 0 
        console.log(a); //0

        let a = 1 && 2 && "123"
        console.log(a) //123;

        let zq = "" && [1] || null || function(){
    }
        console.log(zq); //fun