How can I find objects with same keys values in array?

I have an array of objects that looks like this:

  const arr = [
    { type: 'type', fields: ['field1'] },
    { type: 'type2' },
    { type: 'type', fields: ['field2'] },
  ]

And I need to find objects with the same type to merge fields key in them, like this:

  const arr = [
    { type: 'type', fields: ['field1', 'field2'] },
    { type: 'type2' },
    { type: 'type', fields: ['field1', 'field2'] },
  ]

My plan was to filter through the array, but my problem is that I don’t know which type will send me API, so filtering by item.type wouldn’t work for me.

Answer

If that is the exact solution that you want. Following code snippet may help you.

    const arr = [
      { type: 'type', fields: ['field1']},
      { type: 'type2'},
      { type: 'type', fields: ['field2']}
    ]
    
    const modifyArr = (data) => {
      let res = [];
      arr.map((item) => {
          if(item.type == data.type){
            if(Object.keys(item).includes('fields')){
              res = res.concat(item.fields);
            }
          }
      });
      return Object.keys(data).includes('fields') ? { type: data.type, fields: res } : { type: data.type };

}

let newArr = arr.map(item => modifyArr(item));

console.log(newArr); 

This will print

[
    { type: 'type', fields: ['field1', 'field2'] },
    { type: 'type2' },
    { type: 'type', fields: ['field1', 'field2'] },
  ]