Skip to main content

Grouping Exports in Javascript code

As a Javascript developer, you will come across many occassions when you will have to export many functions, variables or other items from one file and import them in different files. You may end up with a code like the following

export const function1 = () => { /*something here */ } ;
export const function2 = () => { /*something here */ } ;
export const function3 = () => { /*something here */ } ;
export const function4 = () => { /*something here */ } ;
export const function5 = () => { /*something here */ } ;
export const function6 = () => { /*something here */ } ;
export const function7 = () => { /*something here */ } ;
And in the file you want to import you will be importing like the following
import { function1, function2, function3, function5, function6, function7 } from './path_to_the_script'
You can improve it using * if you want to import all the functions.

import * as Functions from './path_to_the_script'
This is a better way of importing all items from a script. I like another approach better which is to group the related exports together and give it a name and import the grouped items. So for example think of a Redux action file which may look like the following


const updateSearch = (payload) = ({type: UPDATE_SAERCH, payload});
const resetSearch = (payload) = ({type: RESET_SEARCH, payload});
const initializeSearch = (payload) = ({type: INIT_SEARCH, payload});
These actions can be exported like the following

export const SearchActions = {
  updateSearch,
  resetSearch,
  initializeSearch 
}
Now in the file where they are needed, we can import SearchActions. The prefix SearchAction in the code will make it clear that from where these actions are coming.

import {SearchActions} from './actions';
 
this.props.dispatch( SearchActions.updateSearch() );
While using this approach the following rules must be followed:


  • Only group together items that are related to each other in some sense e.g all of them are actions for one screen etc. 
  • Any function (action, helper, component) imported in a file MUST NOT be exported again. Exporting imported functions creates a so-called mapper which is against the technical requirements of the project. 
  • A class, function, constant etc may only be exported once. Exporting same item in multiple objects is a bad practice, for example (Notice method average is being exported from two different groups):

const sum = (a, b) = return a+b

const difference = (a, b) = return a-b
const average = (a, b, c) = return (a+b+c)/3

export math = {
    sum,
    difference,
    average      # bad, exported twice!
}
 
export stats = {
    average      # bad, exported twice!
}


What do you think about the approach? Do you have a better idea of importing and exporting items?

Comments

Popular posts from this blog

Html5 Canvas Drawing -- Draw dotted or dashed line

This post is for those who want to use html5 canvas for drawing. The canvas API now has built in methods to create lines with dashes. The method is called setLineDash. Following is the code sample to create dashed line. var canvas = document . getElementById ( "canvas" ); var ctx = canvas . getContext ( "2d" ); ctx . setLineDash ([ 5 , 3 ]); /*Dash width and spaces between dashes.*/ ctx . beginPath (); ctx . moveTo ( 0 , 100 ); ctx . lineTo ( 400 , 100 ); ctx . stroke (); If you want to draw lines having a custom style there is no methos in the API. But fortunately there is a way to achieve this. Following is a description about how I achieved this. You can set the stroke pattern on canvas context. Stroke pattern can be created using any image. You create image for your custom pattern and set strokeStyle of the context like the following: var linePattern; imageToUsedAsPattern.onload = function() { linePattern = context.createPattern(imageToU...

Difference between ng-template, ng-content and ng-container

While working on a very complex feature for a client in which I had to present hierarchical dynamic data in three column layout with ability to expand like google image search on each level, I came across ng-content, which seemed like a perfect fit for the solution I was thinking about implementing. But I got confused between ng-content and ng-container when I saw the generated html while debugging my code in developer console. I further investigated both ng-content and ng-container and decided to write my finding here in my blog for future references. If you are also wondering what are they for, read on. <ng-container> When you have to write different host elements to combine many structural component like the following <div *ngIf="condition"> <div *ngFor="..."> Some content here </div> </div> You get many unintentional host elements which are not required for your layout. It becomes a prolem when you have complex appl...

Angular 2+: ng-content

Have you ever felt the need of writing a component like the following <my-component> <div> Some text here </div> <div> Some text here </div> <div> Some text here </div> <div> Some text here </div> </my-component> Now your intention here is to have your custom component and keep having the additional html that you have written between statring and ending tags. If yes, then you are on the right place. Angular provides an element called ng-content which can used to write configurable components. This is called Component Projection, neaning the content that will be procvided inside the opening and closing brackets will be projected. It will be rendered inside a <ng-content> element. It means that you must include a <ng-content> tag somewhere in your components html template so that the provided content can be projected inside it. So your my-component should have a template like the following // myCompo...