replace for loop in javascript

Question

I'm a bit of a JS noob and I'm currently trying to learn array functions.

When trying to refactor some of my old code I stumbled across this:

export const determineValue = (events) => {
 let eligible = false
 for (const event of events) {
 if (event.eventType === "1") {
 eligible = true
 } else if (event.eventType === "2") {
 eligible = false
 return eligible
 }
 }
 return eligible
}

For this case, "1" and "2" are the only possible values of event.eventType.

How can I write this compactly?

Are there any best practices to consider here?

Thanks in advance for any clarification!

• Ivar: Do different eventType's exist besides "1" and "2"?
• Christian: For this case, no :)
• Ivar: In that case you are basically checking if every element in your array has a property eventType with value "1". So return events.every(event => event.eventType === "1"). Alternatively you can check if there is any property with value "2" and invert the outcome !events.some(event => event.eventType === "2").(There is probably a good duplicate for this somewhere.)
• Ivar: Does this answer your question? check every values in array of object
• Ivar: I see that it isn't entirely identical because you also return false when the array is empty. You can still use .every() or .some(), but you'll need an extra step: events.length === 0 ? false : events.every(event => event.eventType === "1"). (Though just a regular if-statement instead of a conditional operator might be better readable.)

Answer 1

A simplified solution would be

//example setup
const events = [{"eventType":"1"},{"eventType":"2"}];
// Solution 
const eventTypes = events.map(x => x.eventType);
return eventTypes.includes("1") && !eventTypes.includes("2");

Answer 2

Since the eligble events are type 1 - all you need to do is filter the events array for those and then return the length of the filtered array.

const events =[{eventType: 1},{eventType: 1},{eventType: 2},{eventType: 2},{eventType: 1},{eventType: 1}];
const determineValue = (events) => {
 return events.filter(x => x.eventType === 1).length
}
;
console.log(determineValue(events)); // gives 4 events are type 1
console.log(events.length); // gives 6 events in total

To enhance it and you can also pass in the type that you want to count (in case you want to count the ineligible events instead)

const events =[{eventType: 1},{eventType: 1},{eventType: 2},{eventType: 2},{eventType: 1},{eventType: 1}];
const determineValue = (events, value) => {
 return events.filter(x => x.eventType === value).length
}
;
console.log(determineValue(events, 1)); // gives 4 events are type 1
console.log(determineValue(events, 2)); //gives 2 events are type 2
console.log(events.length); // gives 6 events in total

Answer 3

I'd go with something like this :

const determineValue = (events) => {
 return events.length > 0 && !(events.every(input => input.eventType === "2"));
}

If events.length > 0 is false, the part behind the && is not executed, and the function immediately returns false.

Otherwise it checks if every item in events has a value "2" for its property eventType. It returns false if the check succeeds and true if it fails, due to the ! in front of it.

Demo

const events0 =[];
const events1 =[{eventType: "1"}, {eventType: "2"}, {eventType: "1"}];
const events2 =[{eventType: "2"}, {eventType: "2"}, {eventType: "2"}];
const determineValue = (events) => {
 return events.length > 0 && !(events.every(input => input.eventType === "2"));
}
console.log(determineValue(events0));
console.log(determineValue(events1));
console.log(determineValue(events2));