Struct to JSON in JavaScript

structjson.js

/**
 * Copyright 2017, Google, Inc.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @fileoverview Utilities for converting between JSON and goog.protobuf.Struct
 * proto.
 */

'use strict';

function jsonToStructProto(json) {
    const fields = {};
    for (const k in json) {
        fields[k] = jsonValueToProto(json[k]);
    }

    return {fields};
}

const JSON_SIMPLE_TYPE_TO_PROTO_KIND_MAP = {
    [typeof 0]: 'numberValue',
    [typeof '']: 'stringValue',
    [typeof false]: 'boolValue',
};

const JSON_SIMPLE_VALUE_KINDS = new Set([
    'numberValue',
    'stringValue',
    'boolValue',
]);

function jsonValueToProto(value) {
    const valueProto = {};

    if (value === null) {
        valueProto.kind = 'nullValue';
        valueProto.nullValue = 'NULL_VALUE';
    } else if (value instanceof Array) {
        valueProto.kind = 'listValue';
        valueProto.listValue = {values: value.map(jsonValueToProto)};
    } else if (typeof value === 'object') {
        valueProto.kind = 'structValue';
        valueProto.structValue = jsonToStructProto(value);
    } else if (typeof value in JSON_SIMPLE_TYPE_TO_PROTO_KIND_MAP) {
        const kind = JSON_SIMPLE_TYPE_TO_PROTO_KIND_MAP[typeof value];
        valueProto.kind = kind;
        valueProto[kind] = value;
    } else {
        console.warn('Unsupported value type ', typeof value);
    }
    return valueProto;
}

function structProtoToJson(proto) {
    if (!proto || !proto.fields) {
        return {};
    }
    const json = {};
    for (const k in proto.fields) {
        json[k] = valueProtoToJson(proto.fields[k]);
    }
    return json;
}

function valueProtoToJson(proto) {
    if (!proto || !proto.kind) {
        return null;
    }

    if (JSON_SIMPLE_VALUE_KINDS.has(proto.kind)) {
        return proto[proto.kind];
    } else if (proto.kind === 'nullValue') {
        return null;
    } else if (proto.kind === 'listValue') {
        if (!proto.listValue || !proto.listValue.values) {
            console.warn('Invalid JSON list value proto: ', JSON.stringify(proto));
        }
        return proto.listValue.values.map(valueProtoToJson);
    } else if (proto.kind === 'structValue') {
        return structProtoToJson(proto.structValue);
    } else {
        console.warn('Unsupported JSON value proto kind: ', proto.kind);
        return null;
    }
}

module.exports = {
    jsonToStructProto,
    structProtoToJson,
};