处理程序函数中的AWS Lambda Node JS 8.10语法错误

Question

I have below AWS lambda method

NodeJS 8.10.0

// 'use strict';
var fs = require("fs");

class ReadFile{
    constructor(file){
        if(undefined == file){
          this.file = "./index.html";
        }
    }

    content(){
        var buff = fs.readFileSync(this.file);
        return Buffer.from(buff, 'base64').toString('ascii');
    }

}
exports.handler = function (event, context, callback) {
    var f = new ReadFile(event.file);
    callback(null, f.content());
    // callback(null,f.content());
};

I got Syntax error

But Same method is working when I define it in handlers without class like below

exports.handler = function (event, context, callback) {
    if (undefined === event.file) {
        event.file = "index.html";
    }
    var cn = fs.readFileSync(event.file);
    callback(null, Buffer.from(cn, 'base64').toString('ascii'));
    // callback(null,f.content());
};

Got error

{errorMessage=RequestId: a51e4f417 Process exited before completing request}

Answer 1

Looks like problem was in your constructor code. I think that your missing else part of condition. So try to replace

    constructor(file){
       if(undefined == file){
         this.file = "./index.html";
       }
    }

to

    constructor(file){
       if(undefined == file){
         this.file = "./index.html";
       }
       else {
         this.file = file;
       }
    }

Answer 2

It happens because your function finish before than your callback ends its execution. You'll need to put the callback in a setTimeOut to finish its execution. This happens because nodeJS uses blocking execution and the callback doesn't return something.

Try with the following structure:

 exports.handler = function (event, context, callback) { if (undefined === event.file) { event.file = "index.html"; } var cn = fs.readFileSync(event.file); setTimeout(() => { //Timeout to execute the callback callback(null, Buffer.from(cn, 'base64').toString('ascii')); // callback(null,f.content()); }, 10000); }; 

As you can see, I added callback in a timeout to load it. This method become the code to Non-blocking and your main function won't finish without its callback.

If you want to use the first structure, just put all your code in main handler and your callback in a timeout like the example.