Function 在 nodejs 中未定义错误。 我的代码有什么问题？

Question

I created two files, app.js and helpers.js and when I tried to call a function from app.js, I got an error, function is not defined.

The two files are located in the same folder. I think there is a problem the module.exports keyword,

can anyone help me here? Here is the code of the two separate files:

 //app.js const helpers= require('./helpers'); const total= sum(10,20); console.log("total:",total);

 //helpers.js const sum = (a,b)=>{ return a+b; } module.exports={ sum };

And the error i am getting is:

const total= sum(10,20);
             ^

ReferenceError: sum is not defined
    at Object.<anonymous> (E:\testing\app.js:5:14)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1167:10)
    at Module.load (internal/modules/cjs/loader.js:996:32)
    at Function.Module._load (internal/modules/cjs/loader.js:896:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)
    at internal/main/run_main_module.js:17:47

Answer 1

Try this way:

   //app.js

const helpers= require('./helpers');


const total= helpers.sum(10,20);
console.log("total:",total);

//helpers.js

const sum = (a,b)=> {
    return a+b;
}

module.exports = sum;

Answer 2

The problem is that you are exporting your function sum in helpers.js within an object:

// helpers.js

// ...

module.exports = {
    sum
};

If you want to access it from app.js you can either use helpers.sum(...) to access it:

// app.js

const helpers = require('./helpers');


const total = helpers.sum(10, 20);
console.log("total:", total);

... or you can use object deconstruction in the require line:

// app.js

const { sum } = require('./helpers');

// ...

Update

Sure, the answer you posted does work, but from the name helpers.js I assume that you might want to put multiple helper functions into that file. Then, you must use an object export - as mentioned above - in order to export all helper functions.

Answer 3

You can try to edit the way to export the sum function to:

module.exports = sum;

That's because when you define:

module.exports = {...}

it means you're exporting an object, not a function.

Usage:

const sum= require('./helpers');

const total= sum(10,20);
console.log("total:",total);

Answer 4

Finally, I found a my answer.

I just needed to replace the helpers keyword with sum keyword in the first line of app.js and I also removed the curly braces around sum in helpers.js as per other's advice.

The correct code is below

//app.js

const sum= require('./helpers');
const total= sum(10,20);

console.log("total:",total);

and

//helpers.js

const sum = (a,b)=>{
return a+b;
}
module.exports=sum;