filter - How to map with a conditional in Javascript - Stack Overflow

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I'm traversing through an object array:

people = [
  {id:1, name:"Bob", available:false},
  {id:2, name:"Sally", available:true},
  {id:1, name:"Trish", available:false},
]

I want my output to be the names of those available:

["Sally"]

I currently know how to map and extract for a field. How do I add the conditional?

  const peopleAvailable = people.map(person => person.value);

Want to do something like this:

  const peopleAvailable = people.map(person.available => person.value);

I'm traversing through an object array:

people = [
  {id:1, name:"Bob", available:false},
  {id:2, name:"Sally", available:true},
  {id:1, name:"Trish", available:false},
]

I want my output to be the names of those available:

["Sally"]

I currently know how to map and extract for a field. How do I add the conditional?

  const peopleAvailable = people.map(person => person.value);

Want to do something like this:

  const peopleAvailable = people.map(person.available => person.value);

• javascript
• filter

Share Improve this question Follow edited Aug 28, 2019 at 21:25 Kamil Kiełczewski 92.4k3434 gold badges394394 silver badges370370 bronze badges asked Aug 28, 2019 at 21:01 lost9123193lost9123193 11k2727 gold badges8383 silver badges125125 bronze badges

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3 Answers 3

Sorted by: Reset to default 13

You cannot conditionally map with the .map() function alone, however you can use .filter() to achieve what you require.

Calling filter will return a new array where each item in the new array satisfies your filtering criteria (ie people.available === true).

In the case of your code, you can directly chain filter with your existing call to .map() to obtain the desired result:

const people = [{
    id: 1,
    name: "Bob",
    available: false
  },
  {
    id: 2,
    name: "Sally",
    available: true
  },
  {
    id: 1,
    name: "Trish",
    available: false
  },
];

const peopleAvailable = people
.filter(people => people.available)    /* filter available people */
.map(person => person.name)            /* map each person to name */ 

console.log(peopleAvailable);

Try

people.reduce((a,c) => a.concat(c.available ? c.name:[]), [])

people = [
  {id:1, name:"Bob", available:false},
  {id:2, name:"Sally", available:true},
  {id:1, name:"Trish", available:false},
];

let r = people.reduce((a,c) => a.concat(c.available ? c.name:[]), [])

console.log(r);

You can't check the condition in map(). If you put conditions then other elements will be returns as undefined. You can deal with this by applying filter() which allows you to return only those elements which are falls in your condition. So you need to use filter() then use map() on the filtered result.

const array = [{
    id: 1,
    name: "Bob",
    available: false
  },
  {
    id: 2,
    name: "Sally",
    available: true
  },
  {
    id: 1,
    name: "Trish",
    available: false
  },
];

const withFilter = array
.filter((r) => { return r.available; })
.map((m) => { return m.name; });                

console.log(withFilter);

const withOutFilter = array
.map((m) => { if(m.available) { return m.name; } });                

console.log(withOutFilter);

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