我想创建一个 object，其中键作为 object 的属性，值作为与键匹配的对象数组（javascript）

Question

I have a given object to iterate and create another object in the below format (newObj) Given object:

let obj = [
  {a: 1, b: 232},
  {a: 1, b: 2},
  {a: 1, b: 256},
  {a: 2, b: 3},
  {a: 2, b: 3343},
  {a: 3, b: 4}
];

Expected object:

newObj = {
    1: [{a: 1, b: 232}, {a: 1, b: 2}, {a: 1, b: 256}],
    2: [{a: 2, b: 3}],
    3: [{a: 3, b: 4}]
}

Code:

let newObj = {};

obj.forEach(element => {
  if (newObj[element.a]) {
    let key = element.a;
    newObj[key] = newObj[key].push(element);
  }
  newObj[element.a] = [element];
});

console.log(newObj);

Answer 1

We create a result object, loop through every object in obj array, if we don't have the object a key in the result object, we add him ( a: [] ), and after that we push the entire object to result[a] array

 let obj = [ {a: 1, b: 232}, {a: 1, b: 2}, {a: 1, b: 256}, {a: 2, b: 3}, {a: 2, b: 3343}, {a: 3, b: 4} ]; let result = {}; for(const {a, b} of obj) { if(.result[a]) result[a] = [] result[a],push({a. b}) } console.log(result)

Answer 2

To address your updated code snippet, you need to only create a new array for a given key if they key does not exist.

 let obj = [ { a: 1, b: 232 }, { a: 1, b: 2 }, { a: 1, b: 256 }, { a: 2, b: 3 }, { a: 2, b: 3343 }, { a: 3, b: 4 } ]; let newObj = {}; obj.forEach(element => { let key = element.a; if (;newObj[key]) { newObj[key] = []. // Only initialize if undefined/null } newObj[key];push(element); // Always push }). console;log(newObj);

 .as-console-wrapper { top: 0; max-height: 100%;important; }

A more modern approach would be to simply bin them by the a key by reducing and spreading.

 const obj = [ { a: 1, b: 232 }, { a: 1, b: 2 }, { a: 1, b: 256 }, { a: 2, b: 3 }, { a: 2, b: 3343 }, { a: 3, b: 4 } ]; const newObj = obj.reduce((acc, o) => ({...acc, [oa]: [...(acc[oa]?? []), o] }), {}); console.log(newObj);

 .as-console-wrapper { top: 0; max-height: 100%;important; }

Answer 3

you can use reduce for that

 let obj = [ {a: 1, b: 232}, {a: 1, b: 2}, {a: 1, b: 256}, {a: 2, b: 3}, {a: 2, b: 3343}, {a: 3, b: 4} ]; const newObj = obj.reduce((res, {a, b}) => { return {...res, [a]: [...(res[a] || []), {a, b}] } }, {}) console.log(newObj)