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JavaScript Express Basics Parameters, Query Strings, and Modularizing Routes Randomize Cards

Posted by Hanwen Zhang
Hanwen Zhang
20,084 Points

What does this line ' const templateData = { id, text, name };' means in the code? Why do we use { }? what type of data?

const express = require('express');
const router = express.Router();
const { data } = require('../data/flashcardData.json');
const { cards } = data;

router.get( '/', ( req, res ) => {    //redirect users to the random cards, do not need /cards since we already here
  const numberOfCards = cards.length;
  const flashcardId = Math.floor( Math.random() * numberOfCards );
  res.redirect( `/cards/${flashcardId}?side=question` )
});

router.get('/:id', (req, res) => {
    const { side } = req.query;
    const { id } = req.params;
    const text = cards[id][side];
    const { hint } = cards[id];

    if (!side) {
      res.redirect(`/cards/${id}?side=question`);
    }
    const name = req.cookies.username;
    const text - cards[id][side];
    const { hint} = cards [id];

    const templateData = { id, text, name };   // here

    if ( side === 'question' ) {
      templateData.hint = hint;
      templateData.sideToShow = 'answer';
      templateData.sideToShowDisplay = 'Answer';
    } else if ( side === 'answer' ) {
      templateData.sideToShow = 'question';
      templateData.sideToShowDisplay = 'Question';
    }

    res.render('card', templateData);
});

module.exports = router;

3 Answers

Peter Vann
Peter Vann
36,427 Points

Hi Hanwen!

In this video (around 2:20), Andrew explains rather quickly what that syntax is:

https://teamtreehouse.com/library/using-data-and-route-parameters

It is what they call "destructuring" (something new in ES6 JavaScript). It is a sort of shorthand syntax that makes extracting data out of objects (such as the video's JOSN file) easier.

This explains it well:

https://wesbos.com/destructuring-objects

Andrew references this JSON file in the video:

{
    "data": {
        "title": "JavaScript Flashcards",
        "cards": [
            {
                "question": "What language are Express apps written in?",
                "hint": "It starts with a \"J\"",
                "answer": "JavaScript"
            },
            {
                "question": "What is one way a website can store data in a user's browser?",
                "hint": "They are delicious with milk",
                "answer": "Cookies"
            },
            {
                "question": "What is a common way to shorten the response object's name inside middleware?",
                "hint": "It has the same abbreviation as \"resolution\"",
                "answer": "res"
            },
            {
                "question": "How many different values can booleans have?",
                "hint": "Think: binary",
                "answer": "2"
            },
            {
                "question": "Which HTML element can contain JavaScript?",
                "hint": "It starts with an \"s\"",
                "answer": "<script>"
            }
        ]
    }
}

His line of code here:

const { data } = require('../data/flashCards.json');

Takes the data in the JSON file and makes it a JSON object stored in the data variable.

Then he explains that this:

const { cards } = data;

Is just an ES6 shorthand way of doing exactly this, but with slightly less code:

const cards = data.cards;

Which assigns the cards object array from the data object to the variable cards.

Destructuring is also better explained here:

https://teamtreehouse.com/library/destructuring

I highly recommend taking the entire Intro to ES6 course here:

https://teamtreehouse.com/library/introducing-es2015

...if you have not already done so.

I hope that helps.

Stay safe and happy coding!

Jeffrey Holcomb
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.a{fill-rule:evenodd;}techdegree seal-36
Jeffrey Holcomb
Full Stack JavaScript Techdegree Graduate 17,506 Points
Jeffrey Holcomb
.a{fill-rule:evenodd;}techdegree seal-36
Jeffrey Holcomb
Full Stack JavaScript Techdegree Graduate 17,506 Points

Hello Hanwen,

The line 

const templateData = { id, text, name };

assigns a value of type Object to the variable templateData. When passing the templateData object to the pug file, you can gain access to each of the keys (id, text, and name) along with their values.

Sean Gibson
Sean Gibson
38,363 Points
Sean Gibson
Sean Gibson
38,363 Points

That makes sense. But then why are the variables not referenced in the cards.pug file using templateData.hint and templateData.text. Is this another feature of ES2015 that wasn't mentioned in the video?

Jeffrey Holcomb
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Jeffrey Holcomb
Full Stack JavaScript Techdegree Graduate 17,506 Points
Jeffrey Holcomb
.a{fill-rule:evenodd;}techdegree seal-36
Jeffrey Holcomb
Full Stack JavaScript Techdegree Graduate 17,506 Points

Sean, the variable name templateData only exists in the cards.js file. When you pass the templateData object into the cards.pug file, only the key/value pairs are passed. Therefore, referencing the hint or text values in the pug file only requires the use of their individual key names. I hope this helps!