JavaScript data type typeof () and conversion

javascript are weakly type, value, comprising: numbers, strings, Boolean values, and, c ++ and java are strong type; int a = "a", string a = "a" being given; var a; primitive types: boolean number number string string value Boolean undefind null, objects Object, the original values are grouped together; 1. Object system comes into an object, an array, a custom function 2. {} eg three courses => 60 61 62; var a = [60,61 62] index number 0, increment ++, a [0] = 60

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <meta name="viewport" content="width=device-width, initial-scale=1.0">
 6     <title>下标获取数值</title>
 7     <script>
 8 // var a=[60,61,62]
 9 // undefined
10 // a[0]
11 // 60
12 // a[1]
13 // 61
14 // a[2]
15 // 62
16 // a[0]=90
17 // 90
18 // a[0]
19 // 90
20     </script>
21 </head>
22 <body>
23 </body>
24 </html>

Array: the primitive type lined up in the order, the array can have anything inside, primitive type

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <meta name="viewport" content="width=device-width, initial-scale=1.0">
 6     <title>数组,原始类型</title>
 7     <script>
 8 // var a [0,"string",false]
 9 // Uncaught SyntaxError: Unexpected token [
10 // var a=[0,"string",false]
11 // undefined
12 // a[0]
13 // 0
14 // a[1]
15 // "string"
16 // a[2]
17 // false
18     </script>
19 </head>
20 <body> 
21 </body>
22 </html>

Custom object var a1 = 60; var a2 = 61; var a3 = 62; var a = { "a1": 60, "a2": 61, "a3": 62} string representing number var a = {0: 60,1: 61,2: 62} in this array type custom made based on sorting, omitting 0

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <meta name="viewport" content="width=device-width, initial-scale=1.0">
 6     <title>自定义对象</title>
 7     <script>
 8 //     var a1=60;
 9 //     var a2=61;
10 //     var a3=62;
11 //     var a={"a1":60,"a2":61,"a3":62}
12 //     //字符串代表序号
13 // var a={"a1":60,"a2":61,"a3":62}
14 // undefined
15 // a["a1"]
16 // 60
17 // a["a2"]
18 // 61
19 // a["a3"]
20 // 62
21 
22 var a={2:60,3:61,4:62}
23 var a={2:60,3:61,4:62}
24 undefined
25 a[2]
26 60
27 a[3]
28 61
29     </script>
30 </head>
31 <body>  
32 </body>
33 </html>

var a; => undefind var a = null; null object so many different types of data, it is determined by what method? typeof () to help see the data type

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <meta name="viewport" content="width=device-width, initial-scale=1.0">
 6     <title>typeof()查看数据类型</title>
 7     <script>
 8 var a;
 9 undefined
10 typeof(a)
11 "undefined"
12 a=1;
13 1
14 typeof(a)
15 "number"
16 a="a";
17 "a"
18 typeof(a)
19 a=false
20 false
21 typeof(a)
22 "boolean"
23 a=[1];
24 [1]
25 typeof(a)
26 "object"
27 a=null;
28 null
29 typeof(a)
30 "object"
31 var a="1111";
32 undefined
33 typeof(a)
34 "string"
35 var b=Number(b)
36 undefined
37 typeof(b)
38 "number"
39 a=1
40 1
41 b=String(a)
42 "1"
43 typeof(a)
44 "number"
45 typeof(b)
46 "string"
47     </script>
48 </head>
49 <body>
50 </body>
51 </html>

Data type conversion? Original Type: string number number string Boolean Boolean "aaa" => digital number display converter var a = 7; var b = number (a); strong conversion 1+ "1" => "11"

JavaScript data type typeof () and conversion

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