[Web] JavaScript (No.39) data type conversion

Operator


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Arithmetic operator

+ - * / %

Unary operator

Unary operator: an operator with only one operand

Operator binary operator of 5 + 6 operands

++Self plus 1

– self minus 1

  • Prefix + +

    var num1 = 5;
++ num1; 

var num2 = 6;
console.log(num1 + ++ num2);

  • Post + +

    var num1 = 5;
num1 ++;    
var num2 = 6 
console.log(num1 + num2 ++);

  • Guess what?

    var a = 1; var b = ++a + ++a; console.log(b);    
var a = 1; var b = a++ + ++a; console.log(b);    
var a = 1; var b = a++ + a++; console.log(b);    
var a = 1; var b = ++a + a++; console.log(b);

    summary
    Pre + +: add 1 first, then participate in the operation
    Post + +: participate in the operation first, and then add 1
    After the above two are understood, the following two communicate with each other
    Pre: subtract 1 first, and then participate in the operation
    Post: first participate in the operation, then subtract 1
    ​

    Sample code

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Unary operator</title>
</head>
<body>
<script>
    //Unary operator: only one operand is needed.--
    //++: before + +: add before operation / execute after + + after operation / execute before adding
    //--: before --: operation after self subtraction / after execution --: operation before execution / after self subtraction
    // var num = 5;
    // // num --;
    // // console.log(num);
    // // num ++;
    // var num2 = 5;
    // // ++ num2 = 5;
    // // console.log(num,num2);//6,6

    // console.log(num++);//5
    // console.log(++num2);//6

    var num1 = 5;
    ++ num1;
    var num2 = 6;
    console.log(num1 + ++ num2);//
</script>
</body>
</html>

Logical operator (Boolean operator)

&&It is true at the same time as two operands, and the result is true. Otherwise, it is false.
||Or one of the two operands is true, the result is true, otherwise it is false.
! not reversed

Relational operators (comparison operators)

<  >  >=  <= == != === !==

//==The difference between = = = and = = = is that = = only makes value comparison, if the type and value of = = are equal at the same time, then they are equal.
var result = '55' == 55;  	// true
var result = '55' === 55; 	// false value is equal, type is not equal
var result = 55 === 55; 	// true

Assignment Operators

= += -= *= /= %=

For example:
var num = 0;
num += 5; / / equivalent to num = num + 5;

Operator precedence 

Priority from top to bottom
	1. () highest priority
	2. Unary operator + + --!
	3. Operator * /% before +-
	4. Relational operator > ><=
	5. Equality operator = =! = =======
	6. Logical operators First & & then||
	7. Assignment operator

Sample code

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Operator</title>
</head>
<body>
<script>
    /*
    * Operators: symbols for calculating
    * Arithmetic operator: + - * /%.
    * Arithmetic expressions: expressions connected by arithmetic operators
    * ①Unary operator: a symbol + + that can be operated by only one operand.--
    * ②Binary operator: requires two operands var num = 10 + 5;
    * ③Ternary operator: three operands are required. When you write conditional judgment, you can say - > that is, ternary expression.
    * ④Compound operator: + = - = * = / =%.=
    * ⑤Relational operators: > and = = = (not strict equals) = = (strict equals)! = (not strict equals)! = = (not strict equals)
    *              If the equation is true, return true, otherwise return false
    * ⑥Logical operators:
    *              &&And - > has an expression of false, and the whole result is false.
    *              ||Or - > an expression is true, and the whole result is true.
    *              !The result of the expression is true.
    * ⑦Assignment operator:=
    * */
    // var num = 10%3;
    // console.log(num);
    //
    // var num1 = 10;
    // num1 += 10; / / equivalent to num1 = num1 + 10
    // console.log(num1)
    //
    // var num2 = 10;
    // num2 -= 10; / / equivalent to num2 = num1 - 10
    // console.log(num2)
    //
    // var str = "5";
    // var num = 5;
    // console.log(str == num);//true is not strict, the value is compared
    // console.log(str === num);//false is strict, comparing value and data type
    // Console.log (STR! = Num); / / false is not strict. The value is compared.
    // Console.log (STR! = = Num); / / true is strict, comparing value and data class
    // console.log(5 > 3);
    // console.log(5 == 3);

    var num1 = 10;
    var num2 = 20;
    console.log(num1 > num2 && 5 < 6);//false
    console.log(num1 > num2 || 5 < 6);//false

    var flag = true;
    console.log(!flag);

    var str = "100hh";
    console.log(isNaN(str));//true isNaN() only judges the value, not the type

    var sum = (10 + 5) * 10;//Parentheses improve operation level
    console.log(sum);
</script>
</body>
</html>

Posted by Chiaki on Fri, 01 Nov 2019 12:58:53 -0700

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