1. Expression and operator
1. An expression operates on one or more variables or values (operands) and returns a new value
2.Operators can be divided into the following categories:
2.1: Assignment operator: =
2.2: Arithmetic operators: +, -, *, /, %, ++, --, - (negation)
2.3: Combining operators: *=, /=, +=, -=, %=
2.4: Comparison operators: ==, !=, >, >=, <, <=, ===, !==
2.5: Logical operators: &&, ||, !
2.6: String operations: +
3. "===" Absolutely equal: the data types are consistent and the values are equal.
4. "!==" Not absolutely equal: data types are inconsistent or values are not equal
4.1 Inconsistent data types
4.2 Values are not equal
4.3 The data types are inconsistent and the values do not want to wait
Here's how to use the operators:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<body>
<script type="text/javascript">
//" == " 表示等于 " != "表示不等于
var a = ( 15 % 2 == 0)// 结果为false
var b = ( 15 % 2 != 0)//结果为true
//控制台输出结果
console.log(a)
//自增 " ++ " 自减 " -- "
var i = 1
console.log(i++) //结果为1 i++先输出本身在加1
console.log(++i) //结果为3 ++i先自加1后输出
var j=10
j = j+10 // 第一种方法
j += 10 //第二种方法
//两种方法运算结果都一样
console.log(j)
//1-3之间的所有整数之和
var result = 0
result = result + 1
result = result + 2
result = result + 3
result += i
//== ===
console.log(10 == "10") //结果为true
//因为 " == " 运行时会自动把两个值转换为相同类型的值
console.log(10 === "10") //结果为false
console.log("10" === "10") //结果为true
/* 因为 "===" 运行时不仅会判断是否为数据是否相等，
还会判断他们的数据类型是否相同
"===" ：绝对等于：数据类型一致，数值相等*/
console.log("10" !== "10") //结果为false
</script>
</body>
</html>
2. if branch structure
1. Simple if statement
if("conditional expression"){ Statement block! }
As shown below:
2.if...else statement: You can use this statement if you need two results.
if("conditional expression"){ Statement block! } else { Statement block! }
As shown below:
3. Multiple if statements: Use this statement when making multiple judgments
Example: If your JS score is above 80 points, you are very suitable for development. If your score is between 60-80, you are suitable for learning software implementation. If your score is below 60 points, then you are suitable for new media.
The implementation code is shown below:
4. Nested if statements
Example: Use nested branches to find the maximum value of three numbers
The implementation code is shown below:
3. switch branch statement
In a switch construct, automatic type conversion is ignored i.e. the expression must be absolutely equal to a constant
switch statement format:
Example: Simulate an automatic beverage machine. When you enter any integer from 1 to 5, the corresponding beverage will be given and prompted whether to continue purchasing the beverage.
The implementation code is as follows:
