Assign Golang variable to Javascript

Issue

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?

Solution

First, you must use the html/template instead of text/template, as the former provides context-sensitive escaping.

Second, in the template the context must be clear that it is JavaScript code, e.g. it must be inside HTML <script> tag.

See this working example:

type Point struct {
    Name string
    X, Y int
}

func main() {
    t := template.Must(template.New("").Parse(src))

    p := Point{"Center", 100, 200}
    pj, err := json.Marshal(p)
    if err != nil {
        panic(err)
    }

    if err = t.Execute(os.Stdout, string(pj)); err != nil {
        panic(err)
    }
}

const src = `<script>
var point = {{.}};
alert(point);
</script>`

Output (try it on the Go Playground):

<script>
var point = "{\"Name\":\"Center\",\"X\":100,\"Y\":200}";
alert(point);
</script>

As you can see, the point JavaScript variable contains a valid JSON text (a JavaScript Object), properly escaped.

Answered By – icza

Answer Checked By – Willingham (GoLangFix Volunteer)

Leave a Reply

Your email address will not be published.