JS reduce: TypeError: Cannot create property at Array.reduce

Question

I have the following:

let keys = ['a','b','c'];
let vals = ['1','b','h'];
const my_obj = keys.reduce(function(acc,key,i) {
return acc[key]=vals[i];
},{});

logger.log(my_obj);

I would like my_obj to be {a:1,b:b,c:h} .

I'm getting:

TypeError: Cannot create property 'b' on string '1'

at Array.reduce

What am I doing wrong?

Answer 1

If you want to use reduce method then its fine, but you will have to return the accumulator to make it work.

 let keys = ['a', 'b', 'c']; let vals = ['1', 'b', 'h']; const my_obj = keys.reduce(function(acc, key, i) { acc[key] = vals[i]; return acc; }, {}); console.log(my_obj);

But I will suggest to use the simple for loop, because of just the simplicity of problem

 let keys = ['a', 'b', 'c']; let vals = ['1', 'b', 'h']; let my_obj = {}; for (let i = 0; i < keys.length; i++) my_obj[keys[i]] = vals[i]; console.log(my_obj);

Answer 2

You need to return object as acc. In your code you are returning the assigned value

 let keys = ['a', 'b', 'c']; let vals = ['1', 'b', 'h']; const my_obj = keys.reduce(function(acc, key, i) { acc[key] = vals[i]; return acc; }, {}); console.log(my_obj);

Answer 3

return acc[key]=vals[i]; actually return the value of vals[i] ==> you finally get h only on https://playcode.io/ environment.

Updated: in your environment, you got that error because:

• after first run of keys.reduce your next acc will be "1" (return acc[key]= vals[0]} equal return vals[0] which is "1" )
• Now you come to second round of keys.reduce , your acc is "1" then you set acc[key]= vals[1]} equal "1"[b] = vals[1] ==> you got that error

Try this:

 let keys = ['a','b','c']; let vals = ['1','b','h']; const my_obj = keys.reduce(function(acc,key,i) { // return new expanded acc return ({...acc, [key]: vals[i]}) },{}); console.log(my_obj);