Setting state values based on an array value React + ES6

Question

I have a state variable in react as:

this.state = {
    formStatus : {
        approved : true,
        rejected : true,
        pending  : true
    }
}

and a dynamic array whose value can contain either one or all of these values

appliedFilters = ['approved', 'rejected', 'pending']

Now What I want to do is set my state keys to false if the array doesn't contain them.

For example, if the array is ['approved', 'rejected'] then my state should be set as:

this.state = {
    formStatus : {
        approved : true,
        rejected : true,
        pending  : false
    }
}

I want to do it using ES6 map() if possible.

I have done something like this but it is not working:

appliedFilters.map(filter => {
    this.setState(prevState => ({
        formStatus: prevState.formStatus.map(
            status => (status === filter) ? true : false
        )
    }))
})

Andy Ray · Accepted Answer · 2018-09-11 06:01:23Z

3

You can't build an object using a map. And you don't want forEach because there's no need for mutation here. Maps work on (and return) collections. You should use reduce.

const appliedFilters = ['approved', 'rejected']

const state = ['approved', 'rejected', 'pending'].reduce((newState, item) => ({
    ...newState,
    [item]: appliedFilters.includes(item)
}), {});

this.setState(state);

answered Sep 11, 2018 at 6:01

Andy Ray

32.3k16 gold badges114 silver badges151 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

n1stre Over a year ago

this actually doesn't work properly. setting state of invalid structure here.. fix it by this.setState({ formStatus: state })

User 101 Over a year ago

i figured that out...... however can you explain to me the purpose of empty {} in the reduce function you used.

n1stre Over a year ago

It's called 'accumulator'. Read more about it here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

User 101 Over a year ago

@streletss i think you meant initial value. Initialize state with empty object

Andy Ray Over a year ago

Yes it's the initial value, it's what newState will be the first time the reduce callback is executed. It's an object here, but if you were, say, adding numbers together in a reducer, the initial value might just be 0, and you keep adding to it and returning the new accumulated value.

seunggabi · Accepted Answer · 2018-09-11 06:02:38Z

1

It's not possible Array.prototype.map, because the map function return new Array()....

Try do this.

const allFilters = ['approved', 'rejected', 'pending'];
const appliedFilters = ['approved', 'rejected'];

const newState = {};
allFilters.forEach(filter => {
    newState[filter] = appliedFilters.includes(filter);
});

// use!!!
newState;

answered Sep 11, 2018 at 6:02

seunggabi

1,83016 silver badges13 bronze badges

Comments

n1stre · Accepted Answer · 2018-09-11 06:07:08Z

1

You can't call .map on prevState.formStatus. It's an object, not array.
Avoid calling this.setState on every iteration of .map.

You could consider simply doing this:

this.setState(prevState => ({
  formStatus: Object
    .keys(prevState.formStatus)
    .reduce((acc, stat) => ({ ...acc, [stat]: appliedFilters.includes(stat) }), {}) 
}))

answered Sep 11, 2018 at 6:07

n1stre

6,1064 gold badges24 silver badges42 bronze badges

Collectives™ on Stack Overflow

Setting state values based on an array value React + ES6

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related