JSON array string conversion in Golang

I have a JSON array string like,

str = '[{"a":"1","b":"1"},{"a":"2","b":"2"}]'

In JS, I can parse it easily.

let data = JSON.parse(str)
// data is ARRAY[2] [{a:"1", b:"1"}, {a:"2", b:"2"}]

In Golang, how can I parse the string?

Eventually I'd like to validate whether the string is JSON format(object or array) or not.

In Go you would try to unmarshal your data into each of the two types you are interested in testing - array (slice), and object (map). This code will run two tests, one of each type you wanted to test for.

import (
	"encoding/json"
	"fmt"
)

func main() {
	tests := [][]byte{
		[]byte(`[{"a":"1","b":"1"},{"a":"2","b":"2"}]`),
		[]byte(`{"a":"1","b":[{"a":1,"b":2}]}`),
	}

	for _, test := range tests {
		kind, err := getKind(test)
		if err != nil {
			fmt.Printf("Error: %s\n", err)
			continue
		}
		fmt.Printf("%s is type %s\n", string(test), kind)

	}
}

func getKind(d []byte) (string, error) {
	var a []interface{}
	var m map[string]interface{}
	var e error

	e = json.Unmarshal(d, &a)
	if e != nil {
		e = json.Unmarshal(d, &m)
		if e != nil {
			return "", e
		}
		return "map", nil
	}
	return "array", nil
}

OUTPUT

[{"a":"1","b":"1"},{"a":"2","b":"2"}] is type array
{"a":"1","b":[{"a":1,"b":2}]} is type map

package main

import (
	"encoding/json"
	"fmt"
	"reflect"
)

func main() {
	tests := [][]byte{
		[]byte(`[{"a":"1","b":"1"},{"a":"2","b":"2"}]`),
		[]byte(`{"a":"1","b":[{"a":1,"b":2}]}`),
	}
	for _, b := range tests {
		var v interface{}
		err := json.Unmarshal(b, &v)
		if err != nil {
			return
		}
		// use reflect or switch-case
		fmt.Println(string(b), "type is:", reflect.TypeOf(v))

		switch val := v.(type) {
		case []interface{}:
			fmt.Println(val, "is array")
		case map[string]interface{}:
			fmt.Println(val, "is map")
		}
	}
}

// output:
// [{"a":"1","b":"1"},{"a":"2","b":"2"}] type is: []interface {}
// [map[a:1 b:1] map[a:2 b:2]] is array
// {"a":"1","b":[{"a":1,"b":2}]} type is: map[string]interface {}
// map[a:1 b:[map[a:1 b:2]]] is map