The Basics/Utility Classes/ObjectIterator

Reference Documentation

Find reference documentation for ObjectIterator here, or navigate to it via the 'Reference' tab.

How many times have you typed out the classic for (let prop of Object.keys(myObj)) ... mantra? More than three times? Yeah, me too. Here's an easy way to loop over the key-value pairs present in an object:

let props: ObjectIterator<Person> = new ObjectIterator(jasonBourne);

for (let kvPair of props) console.log(`${kvPair.key}: ${kvPair.value}`);

// 'firstName: Jason'
// 'lastName: Bourne'
// 'middleInitial: F'

The Simple Stuff

If you hadn't figured it out from that example, ObjectIterator instances provide the ability to iterate over the key-value pairs of a provided input object, returning KeyValuePairs.

let iter: ObjectIterator = new ObjectIterator({
    key1: "value 1",
    key2: 2,
    key3: false,
    key4: {
        innerKey: "innerVal"
    }
});

for (let kvPair of iter) console.log(kvPair);

//  '{ key: "key1", value: "value 1" }'
//  '{ key: "key2", value: 2 }'
//  '{ key: "key3", value: false }'
//  '{ key: "key4", value: { innerKey: "innerVal" } }'

Type Support

As we alluded to in the first example on this page, if you have more strictly-typed objects you can also pass a type to ObjectIterator.

type Car = {
    name: string,
    price: number,
    horn: string
}

let iter: ObjectIterator<Car> = new ObjectIterator({
    name: "Persephone",
    price: 82000,
    horn: "La Cucaracha"
});

for (let kvPair of iter) console.log(kvPair);

// Prints...
//  '{ key: "name", value: "Persephone" }',
//  '{ key: "price", value: 82000 }',
//  '{ key: "horn", value: "La Cucaracha" }'

A Word of Warning

One small hiccup - in JavaScript, every object (every object) stores its keys as strings. This means that, when attempting to use an object that has (read: appears to have) numeric keys, the keys will be 'coerced' into strings.

I put air quotes around 'coerced' because there isn't actually any type coercion occurring - the keys were always strings.

The only time actual number-to-string coercion occurs is when an array is passed to the ObjectIterator constructor. In this situation, the indices of the elements of the provided array will be returned as strings:

let iter: ObjectIterator = new ObjectIterator([
    "Oh",
    "jeez",
    "Scoob"
]);

for (let kvPair of iter) console.log(kvPair);

//  '{ key: "0", value: "Oh" }',
//  '{ key: "1", value: "jeez" }',
//  '{ key: "2", value: "Scoob" }'