Assign Golang variable to Javascript

user_5170722 0
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Currently I am having an issue related to assign a Golang variable to a Javascript variable. I am using the Golang templates, so, from the backend I sent a JSON variable, just like this:

 var c []models.C
 b, _ := json.Marshal(c)
 err = tpl.ExecuteTemplate(w, "index.gohtml",string(b))

As you see, I have a slice, convert it to Json and then that Json to string, and send it to the template. Then, in the frontend I need to assign that to a variable, and it should be valid JSON, I have this:

var rowData = {{.}};

But, I am getting SyntaxError: expected property name, got '{'

So, my question is: How should I assign that JSON?

go-templates go json javascript
2 Answers

You can write custom template function that will marshal your struct into json. That way you don't have to marshal all your structs in the handler yourself. Especially if you need your struct in HTML template as well as in JS script.

Example using Gin.

In main.go file.

    router := gin.New()
    router.SetFuncMap(template.FuncMap{
        "json": func(s interface{}) string {
            jsonBytes, err := json.Marshal(s)
            if err != nil {
                return ""
            }
            return string(jsonBytes)
        },
    })

In your handler function.

type MyStruct struct {
    Foo string `json:"foo"`
}

func Handler(ctx *gin.Context) {
    myStruct := MyStruct{
        Foo: "test",
    }
    
    ctx.HTML(http.StatusOK, "template-file.go.html", gin.H{
        "MyStruct":   myStruct,
    })
}

Finally in your template.go.html file add a script tag and define here your global variables. Later on you can access them in your JS file.

<script type="text/javascript">
    // NB on JSON.parse and json functions!
    let event = JSON.parse({{ json .MyStruct }});
</script>

// Below you can import your JS file as usual.
<script type="text/javascript" src="/assets/js/index.js"></script>
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