Suppose I could hardcode the following:
const data = [ { a: 0, b: 1}, {a:2,b:3},... ]
But I have the data in an array, and I would like to write something like the following:
const data = my_arr.map((element,index) => { a:element, b:index});
How does one yield this kind of object from an array map?
You just need to add parenthesis around the returned object literal.
const my_arr = [1,2,3,4,5];
const data = my_arr.map((element, index) => ({ a: element, b:index }));
// ^ ^
console.log(data);The reason is that the JavaScript parser rules assume that the { following the => is the start of a function body. To go around this, we wrap the object in () (alternatively we can add a return statement)
Read more here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions#Returning_object_literals
Ah, figured this out.
The anonymous object clashes with the scope operators, so you need to encapsulate the object in a scope block, and pass the object by return from there:
const data = my_arr.map((element,index) => { return {a:element,b:index}});
.map((element,index) => ({a:element,b:index}))You have to add parenthesis around your returned object to differentiate it from a simple block:
const my_arr = [1, 2, 4, 3, 4];
const data = my_arr.map((element, index) => ({ a: element, b: index }));
console.log(data);Or return it explicitly:
const my_arr = [1, 2, 4, 3, 4];
const data = my_arr.map((element, index) => { return { a: element, b: index }; });
console.log(data);I guess it's the same
var my_arr = [...Array(5).keys()]
var result = my_arr.map((element,index) => ({ a: element, b: element + 1 }));
console.log('result', result)So, it works
See output:
var results = [];
[...Array(11).keys()].forEach((el) => {
if (el % 2 === 0) {
results.push({ a: el, b: el + 1 })
}
})
console.log('results',results)