I want to convert an object with indexes as keys, into an array in JavaScript.
For example:
Input: obj ={1: 'banana', 2: 'apple',3:'orange' }
Output: ['orange','apple','banana' ]
I have tried with 'Array.prototype.reverse.apply(obj)', but not able to get the result.
var obj ={1: 'banana', 2: 'apple',3:'orange' };
var res =Array.prototype.reverse.apply(obj);
console.log(res); // return the same object, not reverse
What are the other usages of Array.prototype.reverse()?
You can first convert your almost-array-like object to a real array, and then use .reverse():
Object.assign([], {1:'banana', 2:'apple', 3:'orange'}).reverse();
// [ "orange", "apple", "banana", <1 empty slot> ]
The empty slot at the end if cause because your first index is 1 instead of 0. You can remove the empty slot with .length-- or .pop().
Alternatively, if you want to borrow .reverse and call it on the same object, it must be a fully-array-like object. That is, it needs a length property:
Array.prototype.reverse.call({1:'banana', 2:'apple', 3:'orange', length:4});
// {0:"orange", 1:"apple", 3:"banana", length:4}
Note it will return the same fully-array-like object object, so it won't be a real array. You can then use delete to remove the length property.
This is mine implementation of object rotation
function reverseObject(object) {
var newObject = {};
var keys = [];
for (var key in object) {
keys.push(key);
}
for (var i = keys.length - 1; i >= 0; i--) {
var value = object[keys[i]];
newObject[keys[i]]= value;
}
return newObject;
}
for...in in for (var key in object) { doesn't guarantee order, so you might not get perfect rotation.There is no point of doing this, cause object's properties do not have order. Properties order in objects is not guaranteed in JavaScript;
Since ECMAScript 2015, using the Map object could be an alternative. A Map shares some similarities with an Object and guarantees the keys order:
var reverseObj = function(object) {
var NewObj = {}, keysArr = Object.keys(object);
for (var i = keysArr.length-1; i >= 0; i--) {
NewObj[keysArr[i]] = object[keysArr[i]];
}
return NewObj;
}
