例如有个Json文件，test.json如下

{
    "school": "shantou university",
    "teacher": "Martin",
    "classNum": 10,
    "class": [
        {
            "name": "XiaoMing",
            "score": 98
        },
        {
            "name": "XiaoYao",
            "score": 99
        }
    ]
}

Nodejs读写案例如下：

var iconv = require('iconv-lite');
var fs = require('fs');

function loadjson(filepath)
{
    var data;

    try{

        var jsondata = iconv.decode(fs.readFileSync(filepath, "binary"), "utf8");

        data = JSON.parse(jsondata);

        console.log(data);
    }
    catch(err)
    {
        console.log(err);
    }

    return data;
}


function savejson(filepath, data)
{
    var datastr = JSON.stringify(data, null, 4);

    if (datastr)
    {
        try{
            fs.writeFileSync(filepath, datastr);
        }
        catch(err)
        {
            
        }
    }
}

//读
var data = loadjson('test.json');

//修改数据
for(var i=0; i<data.class.length; i++)
{
    if(data.class[i].name == "XiaoYao")
    {
        data.class[i].score = 100;
    }
}

//写，把XiaoYao同学的分数改为100
savejson('test.json', data)