How to define constants in ReactJS

Question

I have a function that maps text to letters:

sizeToLetterMap: function() { 
     return {
                small_square: 's',
                large_square: 'q',
                thumbnail: 't',
                small_240: 'm',
                small_320: 'n',
                medium_640: 'z',
                medium_800: 'c',
                large_1024: 'b',
                large_1600: 'h',
                large_2048: 'k',
                original: 'o'
            };
}

these letters are used to create flickr photo urls. So, the photoUrl function takes in a image object and size text object and calls the sizeToLetterMap to come up with the letter for that size text.

The function:

photoUrl(image, size_text): function () {
      var size = this.sizeToLetterMap(size_text);
}

I don't think its proper design to have the sizeToLetterMap as a function. I think it fits better as a constant. How can I define constants in ReactJS?

Answer 1

You don't need to use anything but plain React and ES6 to achieve what you want. As per Jim's answer, just define the constant in the right place. I like the idea of keeping the constant local to the component if not needed externally. The below is an example of possible usage.

import React from "react";

const sizeToLetterMap = {
  small_square: 's',
  large_square: 'q',
  thumbnail: 't',
  small_240: 'm',
  small_320: 'n',
  medium_640: 'z',
  medium_800: 'c',
  large_1024: 'b',
  large_1600: 'h',
  large_2048: 'k',
  original: 'o'
};

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

  photoUrl(image, size_text) {
    return (<span>
      Image: {image}, Size Letter: {sizeToLetterMap[size_text]}
    </span>);
  }

  render() {
    return (
      <div className="photo-wrapper">
        The url is: {this.photoUrl(this.props.image, this.props.size_text)}
      </div>
    )
  }
}

export default PhotoComponent;

// Call this with <PhotoComponent image="abc.png" size_text="thumbnail" />
// Of course the component must first be imported where used, example:
// import PhotoComponent from "./photo_component.jsx";

Answer 2

If you want to keep the constants in the React component, use statics property, like the example below. Otherwise, use the answer given by @Jim

var MyComponent = React.createClass({
    statics: {
        sizeToLetterMap: {
            small_square: 's',
            large_square: 'q',
            thumbnail: 't',
            small_240: 'm',
            small_320: 'n',
            medium_640: 'z',
            medium_800: 'c',
            large_1024: 'b',
            large_1600: 'h',
            large_2048: 'k',
            original: 'o'
        },
        someOtherStatic: 100
    },

    photoUrl: function (image, size_text) {
        var size = MyComponent.sizeToLetterMap[size_text];
    }

Answer 3

well, there are many ways to do this in javascript just like other says. I don't think there's a way to do it in react. here's what I would do:

in a js file:

module.exports = {
    small_square: 's',
    large_square: 'q'
}

in your react file:

'use strict';

var Constant = require('constants');
....
var something = Constant.small_square;

something for you to consider, hope this helps