javascript static method
Object.fromEntries()
The Object.fromEntries() static method transforms a list of key-value pairs into an object.
const entries = new Map([
["foo", "bar"],
["baz", 42],
]);
const obj = Object.fromEntries(entries);
console.log(obj);
// Expected output: Object { foo: "bar", baz: 42 }
Syntax
Object.fromEntries(iterable)
Parameters
iterable-
: An iterable, such as an
ArrayorMap, containing a list of objects. Each object should have two properties:0- : A string or symbol representing the property key.
1- : The property value.
Typically, this object is implemented as a two-element array, with the first element being the property key and the second element being the property value.
-
Return value
A new object whose properties are given by the entries of the iterable.
Description
The Object.fromEntries() method takes a list of key-value pairs and returns a new object whose properties are given by those entries. The iterable argument is expected to be an object that implements a [Symbol.iterator]() method. The method returns an iterator object that produces two-element array-like objects. The first element is a value that will be used as a property key, and the second element is the value to associate with that property key.
Object.fromEntries() performs the reverse of entries(), except that Object.entries() only returns string-keyed properties, while Object.fromEntries() can also create symbol-keyed properties.
[!NOTE] Unlike
from(),Object.fromEntries()does not use the value ofthis, so calling it on another constructor does not create objects of that type.
Examples
Converting a Map to an Object
With Object.fromEntries, you can convert from Map to Object:
const map = new Map([
["foo", "bar"],
["baz", 42],
]);
const obj = Object.fromEntries(map);
console.log(obj); // { foo: "bar", baz: 42 }
Converting an Array to an Object
With Object.fromEntries, you can convert from Array to Object:
const arr = [
["0", "a"],
["1", "b"],
["2", "c"],
];
const obj = Object.fromEntries(arr);
console.log(obj); // { 0: "a", 1: "b", 2: "c" }
Object transformations
With Object.fromEntries, its reverse method entries(), and array manipulation methods, you are able to transform objects like this:
const object1 = { a: 1, b: 2, c: 3 };
const object2 = Object.fromEntries(
Object.entries(object1).map(([key, val]) => [key, val * 2]),
);
console.log(object2);
// { a: 2, b: 4, c: 6 }