javascript php variable

1<script type="text/javascript">
2var abc= 'this is text';
3<?php $abc = "<script>document.write(abc)</script>"?>   
4</script>
5<?php echo $abc;?>

1<script type="text/javascript">
2   var php_var = "<?php echo $php_var; ?>";
3</script>

1<script>
2   var res = "success";
3</script>
4<?php
5   echo "<script>document.writeln(res);</script>";
6?>

1<script>
2var p1 = "success";
3</script>
4
5<?php
6echo "<script>document.writeln(p1);</script>";
7?>

1//this is my code 
2
3$value = <<<data
4       <!--instead of writing data we can name it anything 
5       as long as we close it with the same name, 
6       and that name must not be a keyword in javascript -->
7
8        <script>
9         document.write("hello world");
10        </script>
11       data;
12
13so the php variable $value will not store the string "hello world" inside it,
14so the php variable is just a temporary container for the javascript code and nothing else,
15and if we echo the vairable like this:-
16  
17echo $value;
18then hello world will be printed in the browser page,
19and it is the same as using echo to excute a javascript code, so it is as:-
20  
21echo "<script>document.write(\"hello world\")</script>"
22  
23  
24  
25//using console instead of document.write
26  
27$value = <<<inConsole
28        <script>
29         console.log("hello world");
30        </script>
31       inConsole;
32
33
34but the value will not be printed in the console unless we echo the variable, 
35like this:-
36
37echo $value
38then hello world will be printed in the console
39  
40  
41  
42//other examples such as storing data to localstorage
43  
44$local = <<<localstorage
45        <script>
46         localStorage.setItem("anything", "hello");
47        </script>
48        localstorage;
49
50
51but this code will not work until we echo the variable such as:-
52echo $local
53
54and if we open the console and write localstorage then the item anything
55with its value hello will appear
56  
57  
58  
59  
60  
61  
62and if we want to remove the item from localstorage then use this code:-
63
64$local = <<<localstorage
65        <script>
66         localStorage.removeItem("anything");
67        </script>
68        localstorage;
69
70        echo $local;
71
72note: never forget to use the echo statement or the code will not work
73  
74  
75  
76  
77and if we want to get data from localstorage, we use this code
78
79$local = <<<localstorage
80        <script>
81         let a = localStorage.getItem("anything");
82         document.write(a);
83        </script>
84        localstorage;
85
86        echo $local;
87
88then the value of the varaible a will be print in the webpage, 
89