web前端-javascript-运算符(介绍说明，算术运算符、+、-、*、/、%，隐式类型转换、转换为String、转换为Number)

运算符

var a = 123;

var result = typeof a;

console.log(typeof result, "result = " + result);

result = a + 1;
console.log(typeof result, "result = " + result);

result = 456 + 789;
console.log("result = " + result);

result = true + 1;
console.log(typeof result, "result = " + result);

result = true + false;
console.log(typeof result, "result = " + result);

result = 2 + null;
console.log(typeof result, "result = " + result);

result = 2 + NaN;
console.log(typeof result, "result = " + result);

result = "你好" + "大帅哥";
console.log(typeof result, "result = " + result);

var str = "锄禾日当午，" + 
"汗滴禾下土，" + 
"谁知盘中餐，" + 
"粒粒皆辛苦";
console.log("result = " + result);

result = 123 + "1";
console.log(typeof result, "result = " + result);

result = true + "hello";
console.log(typeof result, "result = " + result);

var c = 123;
c = c + "";
console.log(typeof result, "result = " + result);

result = 1 + 2 + "3"; // 33
console.log(typeof result, "result = " + result);

result = "1" + 2 + 3; // 123
console.log(typeof result, "result = " + result);

result = 100 - 5;
console.log("result = " + result);

result = 100 - true;
console.log(typeof result, "result = " + result);

result = 100 - "1";
console.log(typeof result, "result = " + result);

result = 2 * 2;
console.log(typeof result, "result = " + result);

result = 2 * "8";
console.log(typeof result, "result = " + result);

result = 2 * undefined;
console.log(typeof result, "result = " + result);

result = 2 * null;
console.log(typeof result, "result = " + result);

result = 4 / 2;
console.log(typeof result, "result = " + result);

result = 3 / 2;
console.log(typeof result, "result = " + result);

var d = "123";
d = d - 0;
console.log(typeof result, "result = " + result);

result = 9 % 3;
result = 9 % 4;
result = 9 % 5;

console.log("result = " + result);
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1. 操作符说明

运算符也叫操作符

1.1. 通过运算符可以对一个或多个值进行运算,并获取运算结果

比如:typeof 就是运算符，可以用来获得一个值的类型

1.2. 它会将该值的类型以字符串的形式返回

number string boolean undefined object

var a = 123;

var result = typeof a;

console.log(typeof result);
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2. 算数运算符

2.1. 当对非 Number 的值进行运算时，会将这些值转换为 Number 然后再运算

任何值和 NaN 做运算都得 NaN

var result = 2 + NaN;
console.log(typeof result, "result = " + result);
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2.2. +

1. +可以对两个值进行加法运算，并将结果返回
2. 如果对两个字符串进行加法运算，则会做拼串
   • 会将两个字符串拼接为一个字符串，并返回
3. 任何的值和字符串做加法运算，都会先转换为字符串，然后再和字符串做拼串的操作

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

result = 456 + 789;
console.log("result = " + result);

result = true + 1;
console.log(typeof result, "result = " + result);

result = true + false;
console.log(typeof result, "result = " + result);

result = 2 + null;
console.log(typeof result, "result = " + result);

result = 2 + NaN;
console.log(typeof result, "result = " + result);

result = "你好" + "大帅哥";
console.log(typeof result, "result = " + result);

var str = "锄禾日当午，" + "汗滴禾下土，" + "谁知盘中餐，" + "粒粒皆辛苦";
console.log("result = " + result);

result = 123 + "1";
console.log(typeof result, "result = " + result);

result = true + "hello";
console.log(typeof result, "result = " + result);

var c = 123;
c = c + "";
console.log(typeof c, "c = " + c);

result = 1 + 2 + "3"; // 33
console.log(typeof result, "result = " + result);

result = "1" + 2 + 3; // 123
console.log(typeof result, "result = " + result);
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2.3 -

可以对两个值进行减法运算，并将结果返回

var result = 100 - 5;
console.log("result = " + result);

result = 100 - true;
console.log(typeof result, "result = " + result);

result = 100 - "1";
console.log(typeof result, "result = " + result);
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2.4 *

可以对两个值进行乘法运算

var result = 2 * 2;
console.log("result = " + result);

result = 2 * "8";
console.log(typeof result, "result = " + result);

result = 2 * undefined;
console.log(typeof result, "result = " + result);

result = 2 * null;
console.log(typeof result, "result = " + result);
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2.5 /

可以对两个值进行除法运算

var result = 4 / 2;
console.log("result = " + result);

result = 3 / 2;
console.log("result = " + result);
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2.6 %

% 取模运算（取余数）

var result = 9 % 3;
console.log("result = " + result);

result = 9 % 4;
console.log("result = " + result);

result = 9 % 5;
console.log(typeof result, "result = " + result);
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3. 隐式类型转换

3.1 转换为 String

任何值和字符串相加都会转换为字符串，并做拼串操作

1. 我们可以利用这一特点，来将一个任意的数据类型转换 String
   • 我们只需要为任意的数据类型 + 一个"" 即可将其转换为 String
   • 这是一种隐式的类型转换，由浏览器自动完成，实际上它也是调用的 String()函数

var c = 123;
c = c + "";
console.log(typeof c, "c = " + c);

c = null;
c = c + "";
console.log(typeof c, "c = " + c);

c = 1 + 2 + "3"; // 33
console.log(typeof c, "c = " + c);

c = "1" + 2 + 3; // 123
console.log(typeof c, "c = " + c);
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3.2 转换为 Number

1. 任何值做- * / 运算时斗湖以自动转换为 Number
   • 我们可以利用这一特点做隐式的类型转换
2. 可以通过一个值 -0 *1 /1 来将其转换为 Number
   • 原理和 Number()一样，使用起来更加简单

var d = "123";

d = d - 0;
console.log(typeof d, "d = " + d);
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