Create a dynamic number of object keys with "true" values in Javascript

Question

I want to create an object with every value as "true" and the length of keys will be same with array length.

Example :

const myCar = [{name:ford,type:A},{name:opel,type:B}] 

The output want to be like this below

{0:true,1:true}

If the length from the array myCar will be 3 so the output will be like this as well:

{0:true,1:true,2:true}

Answer 1

You can reduce to get a counter and an object

const myCar = [{ name: 'ford', type: 'A' }, { name: 'opel', type: 'B' }];

const myObj = myCar.reduce((acc,_,i) => (acc[i] = true,acc),{});

console.log(myObj);

Breakdown

const myObj = myCar
  .reduce(
    (acc,_,i) => // reduce passes the accumulator, the current object which we ignore here and the index
      (acc[i] = true // set the accumulator at key=index to true 
         ,acc)   // and use the comma operator to return the accumulator
     ,{});       // initialise the accumulator to an empty object

Answer 2

No one seems to be giving you the simple, straightforward approach, so: Just loop from 0 to the length of array (exclusive), adding properties to the object:

const myCar = [{name: "ford",type: "A"},{name: "opel", type: "B"}];

const result = {};
for (let index = 0; index < myCar.length; ++index) {
    result[index] = true;
}
console.log(result);

Answer 3

enjoy!

const myCar = [{name:"ford",type:"A"},{name:"opel",type:"B"}] 
let obj={};
myCar.forEach((item, index)=>{
  obj={...obj,[index]:true};
})
console.log(obj);

Answer 4

Invalid answer:

There are a few ways to achieve what you need. You can either use Array.prototype.map to go through your original array or you can just create a new array based on your first array's length.

An example:

const myCar = [{
  name: 'ford',
  type: 'A'
}, {
  name: 'opel',
  type: 'B'
}];

const myArr = [...new Array(myCar.length)].fill('').map((_, i) => ({
  [i]: true
}));

console.log(myArr);

Quick explanation:

• [...new Array(N)] creates an empty array with N elements
• .fill('') fills it with some data, it does not matter what it is in your case
• .map((_, i)) goes through each entry of the array [i]: true creates a dynamic key with a constant value true

Valid answer:

const myCar = [{
  name: 'ford',
  type: 'A'
}, {
  name: 'opel',
  type: 'B'
}];

const myArr = myCar.reduce((prev, curr, i) => ({ ...prev, [i]: true }), {});

console.log(myArr);