将生成的进程中的数据保存到 Javascript 中的变量中

Question

我在保存生成的 python 进程的结果时遇到问题。将数据转换为 json 后，我在调用 spawn 过程之前将数据推送到函数中定义的数组，但数组一直返回未定义。我可以 console.log 并正确显示数据，但是从函数返回的数组是未定义的。任何投入将不胜感激。提前致谢。

function sonar_projects(){
    const projects = [];
    let obj;
    let str = '';
    const projects_py = spawn('python', ['sonar.py', 'projects']);
    let test = projects_py.stdout.on('data', function(data){
        let projects = [];
        let json = Buffer.from(data).toString()
        str += json
        let json2 = json.replace(/'/g, '"')
        obj = JSON.parse(json2)
        console.log(json2)
        for(var dat in obj){
            var project = new all_sonar_projects(obj[dat].key, obj[dat].name, obj[dat].qualifier, obj[dat].visibility, obj[dat].lastAnalysisDate);
            projects.push(project); 
        }   
        for (var i= 0; i < projects.length; i++){
             console.log(projects[i].key + ' ' + projects[i].name + '  ' + projects[i].qualifier + '  ' + projects[i].visibility + '  ' + projects[i].lastAnalysisDate)
        }
        console.log(projects)
        return projects;
    });  
}

Answer 1

首先，通过 NodeJS 文档，我们有

1. Child Process
2. [child_process.spawn(command, args][, options])
3. Child Process Class
4. Stream
5. Stream Readable Event "data"

即使projects_py.stdout.on(event_name, callback) 接受回调，它也会返回类似EventEmitter 的对象，其中注册了事件（在这种情况下，stdout 调用了它的方法on）或@987654330 @ 元素（ChildProcess 名为 projects_py）。

这是因为每次"data"事件发生时都会调用callback函数。因此，如果事件的分配返回与callback 函数相同，它只会返回一次，然后"data" 事件的下一次发生将由该函数处理，但不会完成.

在这种情况下，我们需要一种方法来收集和编译projects_py.stdout.on("data", callback)事件完成后的数据。 你已经有了收集部分。现在看看另一个：

就在您创建 on "data" 事件之前，我们创建了一个封装该过程的承诺：

    // A promise says "we promise" to have something in the future,
    //  but it can end not happening
    var promise = new Promise((resolve, reject) => {
        // First of all, we collect only the string data
        //  as things can come in parts
        projects_py.stdout.on('data', function(data){
            let json = Buffer.from(data).toString()
            str += json
        });
        
        // When the stream data is all read,
        //  we say we get what "we promised", and give it to "be resolved"
        projects_py.stdout.on("end", () => resolve(str));
        
        // When something bad occurs,
        //  we say what went wrong
        projects_py.stdout.on("error", e => reject(e));
        
    // With every data collected,
    //  we parse it (it's most your code now)
    }).then(str => {
        let json2 = str.replace(/'/g, '"')
        // I changed obj to arr 'cause it seems to be an array
        let arr = JSON.parse(json2)
        //console.log(json2)
        
        const projects = []
        // With for-of, it's easier to get elements of
        //  an object / an array / any iterable
        for(var dat of arr){
            var project = new all_sonar_projects(
                dat.key, dat.name, dat.qualifier,
                dat.visibility, dat.lastAnalysisDate
            );
            projects.push(project); 
        }
        
        // Template strings `a${variable or expression}-/b`
        //  are easier to compile things into a big string, yet still fast
        for(var i = 0; i < projects.length; i++)
            console.log(
                `${projects[i].key} ${projects[i].name} ` +
                `${projects[i].qualifier}  ${projects[i].visibility} ` +
                projects[i].lastAnalysisDate
            )
        console.log(projects)
        
        // Your projects array, now full of data
        return projects;
    // Finally, we catch any error that might have happened,
    //  and show it on the console
    }).catch(e => console.error(e));
}

现在，如果您想对您的一系列项目做任何事情，有两个主要选择：

承诺（then/catch）方式

// Your function
function sonar_projects(){
    // The new promise
    var promise = ...
    
    // As the working to get the projects array
    //  is already all set up, you just use it, but in an inner scope
    promise.then(projects => {
        ...
    });
}

此外，您可以只返回 promise 变量并使用它在 sonar_projects 之外执行承诺（使用 then / catch 和回调）。

异步 / 等待方式

// First of all, you need to convert your function into an async one:
async function sonar_projects(){
    // As before, we get the promise
    var promise = ...
    
    // We tell the function to 'wait' for it's data
    var projects = await promise;
    
    // Do whatever you would do with the projects array
    ...
}