I have a quick question, which I think related to line break or something, but I could not find an answer or post about. Here's an example using reduce() method.
This is what I usually do or see:
const unique = ['a','b','c','a''a','a','b'];
unique.reduce((acc, val)=> {acc[val]=(acc[val]||0)+1; return acc;}, {}); //{ a: 4, b: 2, c: 1 }
However, we can also use this syntax: remove the curly brackets & return, use parentheses instead and add a , before acc. Can someone explain to me this syntax?
unique.reduce((acc, val)=> (acc[val]=(acc[val]||0)+1, acc), {}); // { a: 4, b: 2, c: 1 }
This is because comma operator is used in your example. From MDN:
The comma operator (
,) evaluates each of its operands (from left to right) and returns the value of the last operand.
In (acc[val]=(acc[val]||0)+1, acc) comma does exactly that, it does left part first then returns acc.
Update: Replacing parentheses with curly brackets will not work, because it doesn't comply with JS arrow function syntax. From Arrow function article on MDN:
if the body requires additional lines of processing, you'll need to re-introduce brackets PLUS the "return"
so return is required with curly brackets, while with parentheses it's a concise arrow function which doesn't need return.