1. The operator

General classification:

Unary operatortypeof+ + - -! Binary operator + - * / % == >= <=! = > < | | && ternary operator? :Copy the code

Classification by function:

Arithmetic operators + - * / % logical operators && | |! Comparison operators (relationship) > < = = = = = > = assignment operator = + = - = * = an operator > > < < ~Copy the code

A numeric operation of type number

    var num1 = 1;
    var num2 = 2;
    var num3 = num1 + num2;
    console.log(num3);
    var num4 = 15;
    console.log(num4 % num2);
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+ you can operate on strings in addition to operands and strings are concatenated

    var str1 = "He";
    var str2 = "llo";
    console.log(str1 + str2);
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Comparison operator

The result is a Boolean type

    var num5 = 5;
    var num6 = 6;
    console.log(num6 > num5);
    var num7 = 7;
    // Error
    // console.log(num7>num6>num5);
    // Write it correctly
    console.log(num7 > num6 && num7 > num5);
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The assignment operator

Short form += -= /= *=

    var sum=0;
    sum+=2; // sum = sum+2;
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Add and subtract ++ —

     var num = 10;
    console.log(num++); // assign first and then append
    console.log(num);
    console.log(++num);// add first and then assign
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2. Ternary operators:

Conditions? The condition is established and executed: the condition is not established and executed

The assignment

    var num = 7>3?7:3;
    console.log(num);
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Execute the statement

    var b1= true?console.log(true) :console.log(false);
    console.log(b1);
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Prompt () gets user input

    var num1 = prompt("Please enter a number.") *1; / / 10 01
    
    num1>10? alert(num1):alert("0"+num1);
    
    if(num1>10){
        alert(num1);
    }else{
       alert("0"+num1);
    }
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Ternary operations are nested

     var res=7>3?8>4?8:4:3;
     console.log(res);
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3. Operator priority:

Multiply and divide before addition and subtraction

    var sum = 10 + 7 * 3 + 10;
    console.log(sum);
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After the first && | |

     var res = 7 > 10 && 7 > 3 || 10 > 5 && 3 > 2;
     console.log(res);
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We can use () when we cannot know the exact priority

Operator priority formula (must remember)

The superlative () of the parenthesis members is the second in the list of all entries ++ --! Multiplication and division remaining three, plus or minus four * / % third + - fourth shift five, relation six >>> <<< shift > < >= <= relation is equal to or not equal to row seven ==! = = = =! = = logic eight, nine && assignment | | 7 = + = - = comma members, the lowest level of the same order of priorityCopy the code

thinking

How to calculate: ‘aa’ + 1 + 1-2 && 1-2 > 3 | | ‘aa + 2 > 3 | | (! 2) && 1 + +?

The calculation process is as follows:'aa'+1+1-2&&1-2>3||'aa'+2>3| | (!true) &&1++   // 2 --- bool
       'aa'+1+1-2&&1-2>3||'aa'+2>3||false&&1++    / /! 2
       'aa'+1+1-2&&1-2>3||'aa'+2>3||false&&2      / / 1 + +
       'aa1'+1-2&&1-2>3||'aa'+2>3||false&&2      // 'aa'+1
       'aa11'-2&&1-2>3||'aa'+2>3||false&&2      // 'aa1'+1
       'aa11'-2&&1-2>3||'aa2'>3||false&&2      // 'aa'+2
        NaN-2&&1-2>3||'aa2'>3||false&&2      //'aa11'-2
        NaN &&1-2>3||'aa2'>3||false&&2      // NaN-2
        NaN && -1 >3||'aa2'>3||false&&2      / / 1-2
        false
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The final result is: false;

The following are the steps to solve the problem:

       'aa'+1+1
       // 'aa1'+1
       // 'aa11'

       'aa'+1+3-2
       // 'aa'+1+1
       // 'aa11'
       'aa'+1+3-2
       // 'aa13'-2
       // NaN - 2
       // NaN

       [1.2.3] - 1
       // [1,2,3] --> '1,2,3' -1
       / / '1, 2, 3 - > NaN 1
       [2] -1
       / / '2' - 1
       / / 2 to 1
       / / 1
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Array object operations;

Implicitly to string and then to other types of operations

Equivalent to firing toString

      var a = {
         a:"123"
     }
     a+12;
     
     // a --->'[object Object]' + 12
     // 12---> '[object Object]' + '12'
     //"[object Object]12"
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Implicit transformation:

1: other types are transferred to number

bool undefined null string arrary object

    true 1 
    false 0 
    undefined NaN 
    null 0
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arrary object --> string --> number

All nans except pure numeric characters

2: other types are converted to strings

Put it in quotes' '
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3: Other types go to Boolean

false : false 0 undefined null NaN ''

All others are true

(Operators are important to remember.)