Import JavaScript file and call functions using webpack, ES6, ReactJS

Question

Trying to do something I would think would be very simple. I would like to import an existing JavaScript library and then call it's functions. So for example I would like to import blah.js and then call blah().

import React from 'react';
import {blah} from 'blah/js/blah.js';

class MyClass extends React.Component {
    constructor() {
        super();
    }

    componentDidMount() {
        window.addEventListener('resize', this.handleResize);
    }

    componentWillUnmount() {
        window.removeEventListener('resize', this.handleResize);
    }

    handleResize() {
        blah.blah();
    }

    render() {
          ....
    }
}

export default MyClass;

Just wondering what magical combination of things I have to do to make this work. Maybe I'm just missing the point. The example gives the error "TypeError: _blah.blah is undefined".

Without an example of the file you're trying to import, this is unanswerable. There is nothing wrong with the code you posted, but whether it works would depend on what is exported from blah.js. — loganfsmyth
Check in blah.js if you have named export of blah object. developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Everettss

tobiasandersen tobiasandersen · Accepted Answer · 2016-07-19T22:01:19

Named exports:

Let's say you create a file called utils.js, with utility functions that you want to make available for other modules (e.g. a React component). Then you would make each function a named export:

export function add(x, y) {
  return x + y
}

export function mutiply(x, y) {
  return x * y
}

Assuming that utils.js is located in the same directory as your React component, you can use its exports like this:

import { add, multiply } from './utils.js';
...
add(2, 3) // Can be called wherever in your component, and would return 5.

Or if you prefer, place the entire module's contents under a common namespace:

import * as utils from './utils.js'; 
...
utils.multiply(2,3)

Default exports:

If you on the other hand have a module that only does one thing (could be a React class, a normal function, a constant, or anything else) and want to make that thing available to others, you can use a default export. Let's say we have a file log.js, with only one function that logs out whatever argument it's called with:

export default function log(message) {
  console.log(message);
}

This can now be used like this:

import log from './log.js';
...
log('test') // Would print 'test' in the console.

You don't have to call it log when you import it, you could actually call it whatever you want:

import logToConsole from './log.js';
...
logToConsole('test') // Would also print 'test' in the console.

Combined:

A module can have both a default export (max 1), and named exports (imported either one by one, or using * with an alias). React actually has this, consider:

import React, { Component, PropTypes } from 'react';

Import JavaScript file and call functions using webpack, ES6, ReactJS

3 Answers