elsanussi-s-mneina/how to allow GopherJS functions to be called from Javascript.txt

## how to allow GopherJS functions to be called from Javascript.txt
This was done using GopherJS version numbers: GopherJS 1.17.1+go1.17.3
Date: December 2021
How to use. Assuming you have GopherJS runing and on your path.

Put surround.go, and index.html in the same directory.

Run the following command from that directory:
GOOS=linux gopherjs build surround.go

Open the index.html file, press the button on the screen labelled "Surround". After you press the button,
a piece of text on the screen changes to "(h)" which is the return value from a function in surround.go file.

How does this work?
The trick is to use the js.Global().Set function to create a global variable that Javascript can access.
The second trick is to store the function as a value in a map from string to interface{}.

## index.html
<html>
	<head>

	</head>
<body>
	<h1>Example 1 of calling surround Javascript code</code>
	<p id="exampleLabel">Example text</p>
	<input type="button" id="surroundButton" value="Surround"
         onClick="document.getElementById('exampleLabel').innerText = pet.Su('h')"/>

	<script src="surround.js"></script>
</body>
</html>

## surround.go
package main

import (
	"syscall/js"
)

func main() {
	js.Global().Set("pet", map[string]interface{}{
		"Su": Su,
	})
}

func Su(text string) string {
	return "(" + text + ")"
}
	This was done using GopherJS version numbers: GopherJS 1.17.1+go1.17.3
	Date: December 2021
	How to use. Assuming you have GopherJS runing and on your path.

	Put surround.go, and index.html in the same directory.

	Run the following command from that directory:
	GOOS=linux gopherjs build surround.go

	Open the index.html file, press the button on the screen labelled "Surround". After you press the button,
	a piece of text on the screen changes to "(h)" which is the return value from a function in surround.go file.

	How does this work?
	The trick is to use the js.Global().Set function to create a global variable that Javascript can access.
	The second trick is to store the function as a value in a map from string to interface{}.
	<html>
	<head>

	</head>
	<body>
	<h1>Example 1 of calling surround Javascript code</code>
	<p id="exampleLabel">Example text</p>
	<input type="button" id="surroundButton" value="Surround"
	onClick="document.getElementById('exampleLabel').innerText = pet.Su('h')"/>

	<script src="surround.js"></script>
	</body>
	</html>
	package main

	import (
	"syscall/js"
	)

	func main() {
	js.Global().Set("pet", map[string]interface{}{
	"Su": Su,
	})
	}

	func Su(text string) string {
	return "(" + text + ")"
	}