I got this math.js:

const sum = (a, b) => a + b
const mul = (a, b) => a * b

export default { sum, mul }

then in math.test.js:

const { sum, mul } = require('./math')

test('Adding 1 + 1 equals 2', () => {
  expect(sum(1, 1)).toBe(2)
})

test('Multiplying 1 * 1 equals 1', () => {
  expect(mul(1, 1)).toBe(1)
})

I got this error from jest:

? Adding 1 + 1 equals 2

  TypeError: sum is not a function

    5 | })
    6 | test('Adding 1 + 1 equals 2', () => {
  > 7 |   expect(sum(1, 1)).toBe(2)
    8 | })
    9 |

If I import those function in the test file, jest runs fine. Can't understand proper way to take external function in ES5.

I got this math.js:

const sum = (a, b) => a + b
const mul = (a, b) => a * b

export default { sum, mul }

then in math.test.js:

const { sum, mul } = require('./math')

test('Adding 1 + 1 equals 2', () => {
  expect(sum(1, 1)).toBe(2)
})

test('Multiplying 1 * 1 equals 1', () => {
  expect(mul(1, 1)).toBe(1)
})

I got this error from jest:

? Adding 1 + 1 equals 2

  TypeError: sum is not a function

    5 | })
    6 | test('Adding 1 + 1 equals 2', () => {
  > 7 |   expect(sum(1, 1)).toBe(2)
    8 | })
    9 |

If I import those function in the test file, jest runs fine. Can't understand proper way to take external function in ES5.

• javascript
• ecmascript-5

• 1 Your mixing your module loading up,. require is monjs, try using import instead. – Keith Commented Apr 1, 2019 at 13:43
• 1 ES5 doesn't have modules. They were introduced in ES2015 (sometimes called "ES6"). – T.J. Crowder Commented Apr 1, 2019 at 13:44
• So were the arrow functions, by the way, that's another thing ES5-inpatible here. – mbojko Commented Apr 1, 2019 at 13:47
• sorry guys I've taken an online tutorial....anyways thanks i've caught the problem! – Black.Jack Commented Apr 1, 2019 at 13:49

4 Answers 4

There are two problems:

1. This line probably doesn't do what you think it does:

   export default { sum, mul }
   

2. You're mixing native module syntax (export/import, often called "ESM" for ECMAScript Modules) with CommonJS syntax (require). Use import to import in ESM syntax.

export default { sum, mul } exports a default export that's an object with the properties sum and mul (which would be an odd thing to do with ESM). If that's really want you want to do, fine, but it's not usually best practice. You can't destructure on import, but you can destructure the object after importing it:

// BUT YOU PROBABLY DON'T WANT TO DO THIS, KEEP READING
import math from "./math"; // Imports that default export
cosnt {sum, mul} = math;   // Destructures it into constants

But, normally you'd use named exports, either as you go:

export const sum = (a, b) => a + b
export const mul = (a, b) => a * b

...or all at once (style decision):

const sum = (a, b) => a + b
const mul = (a, b) => a * b

export { sum, mul };

To import named exports, you'd use syntax like you did but with import, not require:

import { sum, mul } from "./math";

That's not destructuring, though it looks similar. It lacks several features of destructuring (nesting, default values, ...).

Alternately you can import a namespace object:

import * as math from "./math";

That will have sum and mul properties on it (which is why you don't normally export an object with JavaScript native modules; anything that really wants one can get a namespace object).

use named export :

export const sum = (a, b) => a + b
export const mul = (a, b) => a * b

or

export {sum,mul}

then

import { sum, mul } from './math'

Replace

const { sum, mul } = require('./math')

with

import { sum, mul } from './math'

You can leave your function declarations as is and change your export to export { add, mul } and as was said above, change your require statement to import.