Usage of comma operators should be avoided JS-0090
Anti-pattern
Minor
5 months ago
—
3 years old
Unexpected use of comma operator
10484 this.$el.toggleClass('active', value)
10485 const transition =
10486 (this.active ? 'to-has-' : 'from-has-') + this.className
10487 typedoc.$html.addClass(transition),10488 setTimeout(function () {
10489 return typedoc.$html.removeClass(transition)
10490 }, 500)Unexpected use of comma operator
10479 __extends(Toggle, _super),
10480 (Toggle.prototype.setActive = function (value) {
10481 if (this.active != value) {
10482 (this.active = value),10483 typedoc.$html.toggleClass('has-' + this.className, value),
10484 this.$el.toggleClass('active', value)
10485 const transition =Unexpected use of comma operator
10435 if (!($signatures.length < 2)) {
10436 this.$container = this.$el.siblings('.tsd-descriptions')
10437 const $descriptions = this.$container.find('> .tsd-description');
10438 (this.groups = []),10439 $signatures.each(function (index, el) {
10440 _this.groups.push(
10441 new SignatureGroup($(el), $descriptions.eq(index))Unexpected use of comma operator
10425 setTimeout(function () {
10426 from.removeClass('fade-out'), to.removeClass('fade-in')
10427 }, 300)
10428 } else to.addClass('current'), typedoc.viewport.triggerResize()10429 this.index = index
10430 }
10431 }),Unexpected use of comma operator
10423 typedoc.viewport.triggerResize()
10424 }),
10425 setTimeout(function () {
10426 from.removeClass('fade-out'), to.removeClass('fade-in')10427 }, 300)
10428 } else to.addClass('current'), typedoc.viewport.triggerResize()
10429 this.index = index
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)) {}