1.算术运算符

• • • / %

var a = 5;
var b = 4;
var c = a + b;
var d = a - b;
var e = a * b;
var f = a / b;
var g = a % b;
console.log("a+b的结果为:", c);
console.log("a-b的结果为:", d);
console.log("a*b的结果为:", e);
console.log("a/b的结果为:", f);
console.log("a%b的结果为:", g);

a + b的结果为: 9
a - b的结果为: 1   
a * b的结果为: 20  
a / b的结果为: 1.25
a % b的结果为: 1

2.自增和自减

++ — ++/—在后：先参与运算，再自增/自减 ++/—在前：先自增/自减，再参与运算

var a = 3;
a++;
console.log(a);
var b = 4;
++b;
console.log(b);

4
5

3.字符串拼接

字符串中的+号代表字符串的拼接

var a = "1" + 1;
var b =  1 + "1";
var c = "1" + "1";
console.log(a,typeof(a));
console.log(b,typeof(b));
console.log(c,typeof(c));

11 string
11 string
11 string

4.算术运算符

如果是纯数字字符串，计算机会自动转其为数字型进行运算 如果有一侧为非数字字符串，结果会为NaN 若想要改变字符串的数据类型，可在字符串后面乘1

var a = 1 + 1;
var b = "1" + 1;
var c = "1" - 1;
var d = "abc" - 1;
var e = 1 - "abc";
var f = 1 * "abc";
var g = 1 / "abc";
var h = "5" * 1;
console.log(a,typeof(a));
console.log(b,typeof(b));
console.log(c,typeof(c));
console.log(d,typeof(d));
console.log(e,typeof(e));
console.log(f,typeof(f));
console.log(g,typeof(g));
console.log(h,typeof(h));

2 number
11 string 
0 number  
NaN number
NaN number
NaN number
NaN number
5 number

5.赋值运算符

=是赋值运算符

var a = 10;
var b = 10;
var c = 10;
var d = 10;
var e = 10;
var f = 10;
console.log(a = a + 1);
console.log(b += 10);
console.log(c -= 2);
console.log(d *= 2);
console.log(e /= 2);
console.log(f %= 2);

11
20
8 
20
5 
0

6.关系运算符

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

比较运算符的结果为布尔值 比较运算符只比较值，不比较数据类型

console.log(3>2);
console.log(3>=2);
console.log(3<2);
console.log(3<=2);
console.log(3==2);
console.log(3!=2);
console.log(3===2);
console.log(3!==2);

true
true 
false
false
false
true 
false
true

7.字符串比较

字符串的比较会将字符串转换为ASCII码，进行比较

console.log("a">"b");
console.log("a"<"b");
console.log("张三"<"李四");
console.log("张三">"李四");

false
true 
true 
false

8.逻辑运算符

&& || ! &&：结果都为真才为真 ||：结果有一个真则为真 ! 结果取反

console.log(5>4 && 5==4)
console.log(5>4 && 5>4)
console.log(5>4 || 4>5)
console.log(5>4 || 4<5)
console.log(!5>4 || 4<5)
console.log(!5<4 && 4<5)

false
true
true
true
true
true

9.三元运算符

语法：条件? 为真返回的数据:为假返回的数据

console.log(5<9?"真":"假");
console.log(5>9?"真":"假");

真
假