digUp nested object selector

digup-ts handles nested objects and arrays, without throwing error Cannot read property 'x' of undefined, while fully supporting typescript.

Features

• Typescript support, for proper code-completion while coding.
• Supported by all browsers
• Light weight
• Supports arrays

If you need more features like setting, removing and transforming nested properties, try dig-ts.

Install

npm i --save digup-ts

Requirements

• TypeScript >= 2.9

Example digUp Usage

import { digUp } from 'digup-ts';

// Let's pretend abc is unpredictable and maybe incomplete.
const response = {a:
                    {b: [
                          {c: 'First'}, 
                          {c: 'Second'}
                        ]
                    }
                  };
let first = digUp(response, 'a', 'b', 0, 'c'); // 'First'
let maybe = digUp(response, 'a', 'b', 9, 'c'); // undefined
let str   = digUp(response, ['a', 'b', 9, 'c'], 'unknown'); // 'unknown'

As you can see, it accepts a default value, like 'unknown'. Just wrap the keys in an array.

Typescript support

Typescript is fully supported, so your editor points out missing properties.

let X = digUp(response, 'X'); // typescript error 'X' doesn't exist...

Array find

The examples below all use the following data:

const response = {
    data: {
        customers: [
            {name: 'A', age:10}, // missing purchases
            {name: 'B', // missing age
                purchases: [
                    {name: 'shoes', price:10}
                ]
            },
            {name: 'C', age:60,
                purchases: [
                    {name: 'flipflops'}, // missing price
                    {name: 'boots', price:20}
                ]
            },
            {}, // missing name + purchases
            {purchases: [{name: 'boots', price:20}]} // missing name
        ]
    }
}

Array.find among keys

Use a function to find a single item in an array.

import { digUp, last } from 'digup-ts';

// Get customer C using a function
const customerC = digUp(response, 'data', 'customers', cust=>cust.name=='C');

// Get price of boots of customer C (or 0 if not found)
const price = digUp(response, 'data', 'customers', cust=>cust.name=='C', 'purchases', pur=>pur.name=='boots', 'price');

// 'last' function is included in digup-ts
const lastSale = digUp(response, 'data', 'customers', last, 'purchases', last); // boots object

Alternatives

If you need more features like setting, removing and transforming nested properties, try dig-ts.

import { dig, last, max } from 'dig-ts';

const summary = dig(response, 'data', 'customers')
    .return(customers => ({
        purchaseCount: customers.collect('purchases').length,
        biggestPurchase: customers.max('purchases', 'price'),
        biggestPurchaseByLastOldCustomer: customers.filter(customer=>customer.age>=60)
            .dig(last, 'products').max('price')
        ,
        topCustomer: customers
                        .find(max('purchases', 'length'))
                        .return(cust=>({
                            name: cust.name,
                            ...dig(cust, 'purchases').return(purchases => ({
                                itemCount: purchases.length,
                                topPurchase: purchases.max('price'),
                                totalPrice: purchases.sum('price')
                            }))
                         }))
        })
    );

summary will be:

{
    purchaseCount: 4,
    biggestPurchase: 20,
    biggestPurchaseByLastOldCustomer: 20,
    topCustomer: {
        name: 'C',
        itemCount: 2,
        topPurchase: 20
        totalPrice: 20
    }
}

Logical expressions are very verbose for long paths.

let c2 = (abc.a && abc.a.b && abc.a.b[9] && abc.a.b[9].c) || 'C-9'

Lodash get(...) is more compact, but removes typescript support.

import { get } from 'lodash';

let c9 = get(abc, 'a.b[1].c', 'C-1');

ts-optchain preserves typescript typings and has an elegant syntax. Unfortunately it requires Proxy. Please consider this option if the browser support suits your project.

import { oc } from 'ts-optchain';

let c1 = oc(abc).b.c('C-1');

With ts-safe you provide an anonymous function and optional default value. Any runtime errors are caught and ignored. However, optional properties might be a problem. Full disclosure: I wrote ts-safe.

import { safe } from 'ts-safe';

let abc = {a:{b:{c:'C'}}}; // Let's pretend abc isn't so predictable.

let c = safe(_=>a.b.c, 'C-default');

More alternatives:

• https://github.com/facebookincubator/idx
• https://github.com/yayoc/optional-chain

License

digup-ts is MIT Licensed.