Find all index based on condition

Question

How can I get all the indexes based on a condition for an array of objects? I have tried the code below, but it's returning only the first occurrence.

a = [
  {prop1:"abc",prop2:"yutu"},
  {prop1:"bnmb",prop2:"yutu"},
  {prop1:"zxvz",prop2:"qwrq"}];
    
index = a.findIndex(x => x.prop2 ==="yutu");

console.log(index);

Answer 1

findIndex will return only one matching index, You can check value against property prop2 using filter

a = [
  {prop1:"abc",prop2:"yutu"},
  {prop1:"bnmb",prop2:"yutu"},
  {prop1:"zxvz",prop2:"qwrq"}];
    
const allIndexes = a
  .map((e, i) => e.prop2 === 'yutu' ? i : -1)
  .filter(index => index !== -1);
  
  console.log(allIndexes);
  // This is one liner solution might not work in older IE ('flatMap')
 const  notSupportedInIE =a.flatMap((e, i) => e.prop2 === 'yutu' ? i : []);
 console.log(notSupportedInIE);

Answer 2

Try Array.reduce

a = [
  {prop1:"abc",prop2:"yutu"},
  {prop1:"bnmb",prop2:"yutu"},
  {prop1:"zxvz",prop2:"qwrq"}];
    
index = a.reduce((acc, {prop2}, index) => prop2 ==="yutu" ? [...acc, index] : acc, []);

console.log(index);

Answer 3

You can use normal for loop and when ever the prop2 matches push the index in the array

const a = [{
    prop1: "abc",
    prop2: "yutu"
  },
  {
    prop1: "bnmb",
    prop2: "yutu"
  },
  {
    prop1: "zxvz",
    prop2: "qwrq"
  }
];

const indArr = [];
for (let i = 0; i < a.length; i++) {
  if (a[i].prop2 === 'yutu') {
    indArr.push(i)
  }

}
console.log(indArr);

Answer 4

The findIndex method returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1, indicating that no element passed the test. - MDN

You can use reduce here:

const a = [
  { prop1: "abc", prop2: "yutu" },
  { prop1: "bnmb", prop2: "yutu" },
  { prop1: "zxvz", prop2: "qwrq" },
];

const result = a.reduce((acc, curr, i) => {
  if (curr.prop2 === "yutu") acc.push(i);
  return acc;
}, []);

console.log(result);

Answer 5

You can simply iterate through objects, e.g.

function getIndexes(hystack, nameOfProperty, needle) {
    const res = new Array();
    for (const [i, item] of hystack.entries()) {
      if (item[nameOfProperty] === needle) res.push(i);
    }
    
    return res;
}

const items =
  [
    {prop1:"a", prop2:"aa"},
    {prop1:"b", prop2:"bb"},
    {prop1:"c", prop2:"aa"},
    {prop1:"c", prop2:"bb"},
    {prop1:"d", prop2:"cc"}
  ];
  
const indexes = getIndexes(items, 'prop2', 'bb');

console.log('Result', indexes);

Answer 6

You can directly use filter without map function

const a = [
  { prop1: "abc", prop2: "yutu" },
  { prop1: "bnmb", prop2: "yutu" },
  { prop1: "zxvz", prop2: "qwrq" },
];

const res = a.filter((item) => {
  return item.prop2==="yutu";
});

console.log(res);