How to use the value of a variable as the key name for key value pair

Question

I have a Calender component, where I would like to mark a date which is the next day (nextDay). I am using react-native-calendars.

export default class CustomCalender extends React.Component {
    render() {
        const today = moment().format("YYYY-MM-DD");
        const nextDay = moment().add(1, 'days').format("YYYY-MM-DD");  // 2017-08-29

        const mark = {
            '2017-08-16': {selected: true, marked: true}
        };

        return (
            <View style={styles.container}>
                <Text style={styles.labelText}>Select a date</Text>
                <Calendar
                    minDate={today}
                    onDayPress={(day) => {
                        console.log('selected day', day)
                    }}

                    markedDates={mark}
                />
            </View>
        )
    }
}

How can I use the data of nextDay (i.e., 2017-08-29) for the mark constant instead of doing like this '2017-08-16'?

I tried this way:

const mark = {
    today: {selected: true, marked: true}
};

But instead of using the value of today (i.e., 2017-08-29), it uses today itself as the name of the key.

use bracket notation, write it like this: `const mark = { [nextDay]: {selected: true, marked: true} };` — Mayank Shukla, Aug 28 '17 at 05:04
Possible duplicate of [Using a variable for a key in a JavaScript object literal](https://stackoverflow.com/questions/2274242/using-a-variable-for-a-key-in-a-javascript-object-literal) — Mayank Shukla, Aug 28 '17 at 06:15

score 0 · Answer 1 · answered Aug 28 '17 at 06:11

0

Define the mark as empty object first. Then assign it.

const today = moment().format("YYYY-MM-DD");
const mark = {};
mark[today] = {selected: true, marked: true};

Rereference: JavaScript set object key by variable

answered Aug 28 '17 at 06:11

Hana Alaydrus

2,225
16
19

score 0 · Answer 2 · answered Aug 28 '17 at 08:00

A simple example might help you to understand it much better:

let foo = 'hello';
let bar = {};

//using the value stored inside foo as a key for the object
bar[foo] = 'world';
console.log(bar);

//using 'foo' directly as a key instead of the value it stored
bar = {
  foo: 'world'
}
console.log(bar);

How to use the value of a variable as the key name for key value pair

2 Answers2