What is the best way to retrieve a property value from an object using the .find() method?

I've encountered a problem with the following code snippet in my function:

let packName: string = respPack.find(a => {a.id == 'name_input'}).answer.replace(/ /,'_');

My goal is to locate an object by matching its id and retrieve the value stored in its answer property. However, I keep receiving an error message stating:

cannot read property answer of undefined.

I am unsure if I'm going about this the correct way. To provide more context, here is the remainder of my function for better understanding:

saveResponses(){
    const respPack = this.ResponseList;
    const sendTarget: FirebaseObjectObservable<any> = this.afdb.object('/submissions');

    let dataLoad:{ [prop : string]: Array<any> } = {};
    let packName: string = respPack.find(a => {a.id == 'name_input'}).answer.replace(/ /,'_');

    respPack.forEach( a => {
        if(a.answer){
            let data = { question: a.question, answer: a.answer, id: a.id };
            dataLoad[packName].push(data);
        }
        else if(a.responses){
            let dataChunk = { question: a.question, id: a.id, responses: Array<any> }; 

            a.responses.forEach(resp => {
                let respChunk = { response: resp.response, value: resp.value, id: resp.id };
                dataChunk.responses.push(respChunk);
            });
            dataLoad[packName].push(dataChunk);
        }
    });

    sendTarget.set(dataLoad);
}

Answer №1

When using an arrow function with curly braces {}, remember to include the return keyword.

For example:

a => {return a.id == 'name_input'} 

It's important to note that if no items are found, the find method will return undefined, so you need to handle those cases accordingly.

Here's a complete example for better understanding:

let packName: string = "";
let foundElement = respPack.find(a => {
                               return a.id == 'name_input';
                             });
if(foundElement){
    packName = foundElement.answer.replace(/ /,'_');
}

If you prefer keeping it in one line, you can use the following code snippet:

let packName: string = ((respPack.find(a => a.id == 'name_input') || {}).answer || "").replace(/ /,'_');

Answer №2

When using yourArray.find(element), it will return the specific element. Here's an example:

Learn more about find() method

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findhttps://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find

var inventory = [
    {name: 'apples', quantity: 2},
    {name: 'bananas', quantity: 0},
    {name: 'cherries', quantity: 5}
];

function findCherries(fruit) { 
    return fruit.name === 'cherries';
}

console.log(inventory.find(findCherries)); 
// { name: 'cherries', quantity: 5 }

If you're facing issues with your find method, check this section here:

a => {return a.id == 'name_input'} 

For further understanding of arrow functions, see this link:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions

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