Performing JSON Operations Using JSVM-API

Introduction

This topic walks you through on how to use JSVM-API to manipulate data in JavaScript Object Notation (JSON).

Basic Concepts

• JSON (JavaScript Object Notation): a common data exchange format for data transfer, storage, and communication between the frontend and backend. It interacts with multiple programming languages and is widely used in JavaScript for data processing.

Available APIs

API	Description
OH_JSVM_JsonParse	Parses a JSON string and stores the result in a JSON object.
OH_JSVM_JsonStringify	Converts a JS object into a JSON string stores the result in a JSVM string object.

Example

If you are just starting out with JSVM-API, see JSVM-API Development Process. The following demonstrates only the C++ code involved in related APIs.

OH_JSVM_JsonParse & OH_JSVM_JsonStringify

Use OH_JSVM_JsonParse to parse a JSON object and OH_JSVM_JsonStringify to output the parsing result.

CPP code:

// hello.cpp
#include <string>

// Parse a JSON number.
static JSVM_Value JsonParseNumber(JSVM_Env env, JSVM_CallbackInfo info)
{
    // Set the JSON number to be parsed.
    std::string strNumber = "10.555";
    JSVM_Value jsonString = nullptr;
    JSVM_CALL(OH_JSVM_CreateStringUtf8(env, strNumber.c_str(), strNumber.size(), &jsonString));
    JSVM_Value jsonObject = nullptr;
    // Call OH_JSVM_JsonParse to parse the JSON number and store the result in a JSON object.
    JSVM_CALL(OH_JSVM_JsonParse(env, jsonString, &jsonObject));
    double number = 0.0f;
    JSVM_CALL(OH_JSVM_GetValueDouble(env, jsonObject, &number));
    OH_LOG_INFO(LOG_APP, "Test JSVM jsonParseNumber: %{public}f", number);
    return nullptr;
}

// Parse a JSON object.
static JSVM_Value JsonParseObject(JSVM_Env env, JSVM_CallbackInfo info)
{
    // Set the JSON object string to be parsed.
    std::string strObject = "{\"first\": \"one\", \"second\": \"two\", \"third\": \"three\"}";
    JSVM_Value strJson = nullptr;
    JSVM_CALL(OH_JSVM_CreateStringUtf8(env, strObject.c_str(), strObject.size(), &strJson));
    JSVM_Value jsonObject = nullptr;
    // Call OH_JSVM_JsonParse to parse the JSON string object and store the result in a JSON object.
    JSVM_CALL(OH_JSVM_JsonParse(env, strJson, &jsonObject));
    JSVM_Value jsonString = nullptr;
    // Call OH_JSVM_JsonStringify to convert the object into a string and store the string in a JSVM string object.
    JSVM_CALL(OH_JSVM_JsonStringify(env, jsonObject, &jsonString));
    size_t totalLen = 0;
    JSVM_CALL(OH_JSVM_GetValueStringUtf8(env, jsonString, nullptr, 0, &totalLen));
    size_t needLen = totalLen + 1;
    char* buff = new char[needLen];
    JSVM_CALL(OH_JSVM_GetValueStringUtf8(env, jsonString, buff, needLen, &totalLen));
    OH_LOG_INFO(LOG_APP, "Test JSVM jsonParseObject: %{public}s", buff);
    delete[] buff;
    return nullptr;
}

// Register JsonParse callbacks.
static JSVM_CallbackStruct param[] = {
    {.data = nullptr, .callback = JsonParseNumber},
    {.data = nullptr, .callback = JsonParseObject},
};

static JSVM_CallbackStruct *method = param;

JSVM_PropertyDescriptor descriptor[] = {
    {"jsonParseNumber", nullptr, method++, nullptr, nullptr, nullptr, JSVM_DEFAULT},
    {"jsonParseObject", nullptr, method++, nullptr, nullptr, nullptr, JSVM_DEFAULT},
};

// JS code to be executed.
static const char *srcCallNative = R"JS(jsonParseNumber();jsonParseObject();)JS";

Expected result:

Test JSVM jsonParseNumber: 10.555000

Test JSVM jsonParseObject: {"first":"one","second":"two","third":"three"}