如何在Node.js中的多个文件中获取变量的当前值？

Question

I'm using a index.js file and a check.js file in Node.js. I use check.js to check every 500 ms if some value in my databases has changed. If so, the value of variable currentInput changes. I want to use this variable currentInput in index.js so, that I get the current value of it. I tried searching about in but the solutions I've found don't give me the current value back.

In check.js:

var currentInput;
.
.
.

var check = function(){
    pool.query('SELECT someValue FROM table WHERE id=1',function(err,rows){
        if(err) throw err;
        var newInput = rows[0].someValue;
        if(currentInput!=newInput){
            currentInput=newInput;
            }
        console.log('Current value:', currentInput);
    });
    setTimeout(check, 500);
}

In index.js I'd like to use it something like:

var x = function(currentInput);

Answer 1

You can export your function as a module. Then load it and call from index.js.

check.js

exports.check = function() {
    pool.query('SELECT someValue FROM table WHERE id=1',function(err,rows){
        if(err) throw err;
        var newInput = rows[0].someValue;
        if(currentInput!=newInput){
            currentInput=newInput;
        }
        return currentInput);
    });  
};

index.js

var check = require("./path/to/check.js");

setTimeout(function(){
    var x = check.check;
}, 500);

Answer 2

You can use the GLOBAL variable. The GLOBAL variable is (yes you were right) global.

For example:

//set the variable
global.currentInput = newInput;
// OR
global['currentInput'] = newInput;

//get the value
var x = global.currentInput;
// OR
var x = global['currentInput'];

Note that this may not be the most efficient way of doing this, and people do not like this way at all ( https://stackoverflow.com/a/32483803/4413576 )

To use the global variable in different files, they have to be "connected with each other".

// index.js
require('./check.js')