Usage of comma operators should be avoided JS-0090
Anti-pattern
Minor
10 months ago
—
3 years old
Unexpected use of comma operator
1094 const pick = (obj, arr) =>
1095 arr.reduce(
1096 (acc, record) => (
1097 record in obj && (acc[record] = obj[record]), acc1098 ),
1099 {}
1100 );Unexpected use of comma operator
626 const pick = (obj, arr) =>
627 arr.reduce(
628 (acc, record) => (
629 record in obj && (acc[record] = obj[record]), acc 630 ),
631 {}
632 );Unexpected use of comma operator
18 var userlist = [];
19 const pick = (obj, arr) =>
20 arr.reduce(
21 (acc, record) => (record in obj && (acc[record] = obj[record]), acc), 22 {}
23 );
24 data.forEach((item) => userlist.push(pick(item, ["id", "username"])));Unexpected use of comma operator
13 var raporlist = [];
14 const pick = (obj, arr) =>
15 arr.reduce(
16 (acc, record) => (record in obj && (acc[record] = obj[record]), acc),17 {}
18 );
19 data.forEach((item) => raporlist.push(pick(item, ["id", "username"])));
Description
The comma operator includes multiple expressions where only one is expected. It evaluates each operand from left to right and returns the value of the last operand. However, this frequently obscures side effects, and its use is often an accident. Here are some examples of sequences:
Bad Practice
let a = (3, 5); // a = 5
a = b += 5, a + b;
while (a = next(), a && a.length);
(0, eval)("doSomething();");
res = doSomething(), val;
0, eval("doSomething();");
do {} while (doSomething(), !!test);
for (; doSomething(), !!test; );
if (doSomething(), !!test);
switch (val = func(), val) {}
while (val = func(), val < 42);
with (doSomething(), val) {}
Recommended
res = (doSomething(), val);
(0, eval)("doSomething();");
do {} while ((doSomething(), !!test));
for (i = 0, j = 10; i < j; i++, j--);
if ((doSomething(), !!test));
switch ((val = func(), val)) {}
while ((val = func(), val < 42));
with ((doSomething(), val)) {}