Looping through JSON data to add nested data to array (to be added to MySQL database table) fails at missing value

Question

I have this 4-tier if loop which loops through a JSON object from a file. The aim here is to create an array which will be added to a row of a MySQL database.

The loop should filter through the json and then add certain values to an array:

var content = fs.readFileSync("dataSubcats.json");
var jsonContent = JSON.parse(content);

var values = [];

for(let i=0; i<jsonContent.length; i++) {

    if (jsonContent[i].subcategories) {
        let subcat = jsonContent[i].subcategories.length;
        for (let n=0; n<subcat; n++) {

            if(jsonContent[i].subcategories[n]) {
                let subsubcat = jsonContent[i].subcategories[n].facetValueData.length
                for (let p=0; p<subsubcat; p++) {

                    if(jsonContent[i].subcategories[n].facetValueData) {
                        let products = jsonContent[i].subcategories[n].facetValueData[p].productData.length
                        for (let f=0; f<products; f++) {
                            
                            var productDataFinal = jsonContent[i].subcategories[n].facetValueData[p].productData[f]
                            values.push([   
                                jsonContent[i].id, jsonContent[i].categoryName, 
                                jsonContent[i].subcategories[n].name, jsonContent[i].subcategories[n].code, 
                                jsonContent[i].subcategories[n].facetValueData[p].name, jsonContent[i].subcategories[n].facetValueData[p].code,
                                productDataFinal.productDisplayName, productDataFinal.code, 
                                productDataFinal.url, productDataFinal.imageUrl,
                                productDataFinal.price.value, productDataFinal.originPrice.value, 
                                productDataFinal.price.currencyIso, productDataFinal.inStock,
                                productDataFinal.newProduct
                            ])
                        }
                    }
                }
            } else {
                 console.log(`No facetvalue data found at ${jsonContent[i]}`)
        }
        } 
    } else {
        console.log(`No subcats found at ${jsonContent[i]}`)
    }
}

The JSON structure is as follows:

 [
    {
        "id": 0,
        "categoryName": "Beauty",
        "subcategories": [
            {
                "count": 2688,
                "code": "/beauty/skin-care",
                "name": "Skincare",
                "facetValueData": [
                    {
                        "count": 682,
                        "code": "/beauty/skin-care/lotion-serum-and-essence",
                        "name": "Lotion Serum & Essence",
                        "productData": []
                    },
                    {
                        "count": 497,
                        "code": "/beauty/skin-care/moisturiser-and-mist",
                        "name": "Moisturiser & Mist",
                        "productData": []
                    },
                    {
                        "count": 354,
                        "code": "/beauty/skin-care/cleanser-and-exfoliation",
                        "name": "Cleanser & Exfoliation",
                        "productData": []
                    },
                    {
                        "count": 345,
                        "code": "/beauty/skin-care/mask-and-treatment",
                        "name": "Mask & Treatment",
                        "productData": []
                    }
                ]
            },
            {
                "count": 1549,
                "code": "/beauty/makeup",
                "name": "Makeup",
                "facetValueData": [
                    {
                        "count": 653,
                        "code": "/beauty/makeup/face",
                        "name": "Face",
                        "productData": []
                    },
                    {
                        "count": 460,
                        "code": "/beauty/makeup/makeup-lips",
                        "name": "Lips",
                        "productData": []
                    },
                    {
                        "count": 337,
                        "code": "/beauty/makeup/eyes",
                        "name": "Eyes",
                        "productData": []
                    },
                    {
                        "count": 124,
                        "code": "/beauty/makeup/makeup-cheeks",
                        "name": "Cheeks",
                        "productData": []
                    }
                ]
            }
        ]
    },
    {
        "id": 1,
        "categoryName": "Electronics",
        "subcategories": [
            {
                "count": 526,
                "code": "/electronics/audio-devices",
                "name": "Audio",
                "facetValueData": [
                    {
                        "count": 153,
                        "code": "/electronics/audio-devices/speakers",
                        "name": "Speakers",
                        "productData": []
                    },
                    {
                        "count": 145,
                        "code": "/electronics/audio-devices/earphones",
                        "name": "Earphones",
                        "productData": []
                    },
                    {
                        "count": 142,
                        "code": "/electronics/audio-devices/headphones",
                        "name": "Headphones",
                        "productData": []
                    },
                    {
                        "count": 51,
                        "code": "/electronics/audio-devices/true-wireless-and-airpods",
                        "name": "True Wireless & Airpods",
                        "productData": []
                    }
                ]
            }
                    
        ]
    }
]

it continues like this for a total of 10 categoryName objects (I may have gotten some closing brackets wrong here but it is correct in my script).

The loop always breaks with the following error:

let subsubcat = jsonContent[i].subcategories[n].facetValueData.length
                                                                               ^

TypeError: Cannot read property 'length' of undefined
    at Object.<anonymous> (/Users/Desktop/NodeScraper/db.js:18:80)
    at Module._compile (internal/modules/cjs/loader.js:1137:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1157:10)
    at Module.load (internal/modules/cjs/loader.js:985:32)
    at Function.Module._load (internal/modules/cjs/loader.js:878:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)
    at internal/main/run_main_module.js:17:47

I am stumped

Could you share the code that tries to get the content from the file? — gustavozapata
– gustavozapata, Commented Aug 18, 2020 at 16:16
When I check the JSON, the subcategories array is not closed. The same goes for facetValueData. Can that be the problem? Or is that just an copy-paste error? — Bas
– Bas, Commented Aug 18, 2020 at 16:21
The JSON is actually much longer than this, this is just for an example — tomj1596
– tomj1596, Commented Aug 18, 2020 at 16:22

Giovanni Esposito · Accepted Answer · 2020-08-18 16:26:11Z

1

Ciao, you error could be here:

for (let n=0; n<subcat; i++) {...}

try to replace i with n like:

for (let n=0; n<subcat; n++) {...}

answered Aug 18, 2020 at 16:26

Giovanni Esposito

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4 Comments

tomj1596 Over a year ago

Thank you, I have changed my code as per your suggestion, unfortunately the error still persists

tomj1596 Over a year ago

The error now says

let subsubcat = jsonContent[i].subcategories[n].facetValueData.length                                                                                ^  TypeError: Cannot read property 'length' of undefined

tomj1596 Over a year ago

I have figured it out, the if Statement "if(jsonContent[i].subcategories[n].facetValueData)" should have been above the for loop just before it, not below. Thanks for help

Giovanni Esposito Over a year ago

No problem. If you think answer was useful please, mark it as valid :).

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