adding values from an array to object javascript

Question

I have an array.

var nestedArr =[['loop0', 0], ['loop1', 1], ['loop2', 2], ['loop3', 3], ['loop4', 4], ['loop5', 5]]

I have to get using for loop this:

var obj = { loop0: 0, loop1: 1, loop2: 2 ...};

I am trying this :

for(var j = 0; j < nestedArr.length; j++){
 obj[nestedArr[j][0]] = nestedArr[j][1]}

but I am getting values as undefined. How do I add values correctly.

• Mario Murrent: Can you provide a code snippet on jsFiddle or something similar? I dont really understand your problem.
• Nina Scholz: with a declared and initialized var obj = {}, the code works.

Answer 1

Working fine for me. Just added the definition of obj

var nestedArr =[['loop0', 0], ['loop1', 1], ['loop2', 2], ['loop3', 3], ['loop4', 4], ['loop5', 5]],
 obj = {};
for(var j = 0; j < nestedArr.length; j++){
obj[nestedArr[j][0]] = nestedArr[j][1]
}
console.log(obj)

• Nina Scholz: it does not explain why but I am getting values as undefined.
• Muhammad Usman: because it is not giving you undefined

Answer 2

You can use reduce function as below:

var nestedArr = [
 ['loop0', 0],
 ['loop1', 1],
 ['loop2', 2],
 ['loop3', 3],
 ['loop4', 4],
 ['loop5', 5]
];
var output = {};
nestedArr.reduce(function(itm) {
 output[itm[0]] = itm[1];
});
console.log(output);

Your loop also is correct:

var nestedArr = [
 ['loop0', 0],
 ['loop1', 1],
 ['loop2', 2],
 ['loop3', 3],
 ['loop4', 4],
 ['loop5', 5]
];
var obj = {};
for (var j = 0; j < nestedArr.length; j++) {
 obj[nestedArr[j][0]] = nestedArr[j][1]
}
console.log(obj)

• CertainPerformance: I wasn't the downvoter, but .map is not appropriate when you aren't returning anything - use .reduce instead
• Nina Scholz: map ... without using the result. btw the given code of op works.
• Saeed: I change it to reduce
• CertainPerformance: @Satpal Why forEach? If reducing an array into an object, that's exactly what reduce is for
• Saeed: Your for loop is correct and you see it runs well. whats the problem? @blahblahvah

Answer 3

Using Array.prototype.reduce you can do this.

var nestedArr =[['loop0', 0], ['loop1', 1], ['loop2', 2], ['loop3', 3], ['loop4', 4], ['loop5', 5]]
const res = nestedArr.reduce((acc, v) => {
 acc[v[0]] = v[1];
 return acc;
}, {});
console.log(res);