When returning an object from an arrow function, it seems that it is necessary to use an extra set of {} and a return keyword because of an ambiguity in the grammar.
That means I can’t write p => {foo: "bar"}, but have to write p => { return {foo: "bar"}; }.
If the arrow function returns anything other than an object, the {} and return are unnecessary, e.g.: p => "foo".
p => {foo: "bar"} returns undefined.
A modified p => {"foo": "bar"} throws “SyntaxError: unexpected token: ':'”.
Is there something obvious I am missing?
Solution 1
You must wrap the returning object literal into parentheses. Otherwise curly braces will be considered to denote the functions body. The following works:
p => ({ foo: 'bar' });
You don't need to wrap any other expression into parentheses:
p => 10;
p => 'foo';
p => true;
p => [1,2,3];
p => null;
p => /^foo$/;
and so on.
Reference: MDN - Returning object literals
Solution 2
You may wonder, why the syntax is valid (but not working as expected):
var func = p => { foo: "bar" }
It's because of JavaScript's label syntax:
So if you transpile the above code to ES5, it should look like:
var func = function (p) {
foo:
"bar"; //obviously no return here!
}
Solution 3
If the body of the arrow function is wrapped in curly braces, it is not implicitly returned. Wrap the object in parentheses. It would look something like this.
p => ({ foo: 'bar' })
By wrapping the body in parens, the function will return { foo: 'bar }.
Hopefully, that solves your problem. If not, I recently wrote an article about Arrow functions which covers it in more detail. I hope you find it useful. Javascript Arrow Functions
Solution 4
Issue:
When you do are doing:
p => {foo: "bar"}
JavaScript interpreter thinks you are opening a multi-statement code block, and in that block, you have to explicitly mention a return statement.
Solution:
If your arrow function expression has a single statement, then you can use the following syntax:
p => ({foo: "bar", attr2: "some value", "attr3": "syntax choices"})
But if you want to have multiple statements then you can use the following syntax:
p => {return {foo: "bar", attr2: "some value", "attr3": "syntax choices"}}
In above example, first set of curly braces opens a multi-statement code block, and the second set of curly braces is for dynamic objects. In multi-statement code block of arrow function, you have to explicitly use return statements
For more details, check Mozilla Docs for JS Arrow Function Expressions
Solution 5
ES6 Arrow Function returns an Object
the right ways
- normal function return an object
const getUser = user => {return { name: user.name, age: user.age };};
const user = { name: "xgqfrms", age: 21 };
console.log(getUser(user));
// {name: "xgqfrms", age: 21}
- (js expressions )
const getUser = user => ({ name: user.name, age: user.age });
const user = { name: "xgqfrms", age: 21 };
console.log(getUser(user));
// {name: "xgqfrms", age: 21}
explain
refs
https://github.com/lydiahallie/javascript-questions/issues/220
https://mariusschulz.com/blog/returning-object-literals-from-arrow-functions-in-javascript
Solution 6
You can always check this out for more custom solutions:
x => ({}[x.name] = x);
