这是JavaScript逗号运算符的一种情况

Question

Please see this code from d3.js

if (y1 < y0) t = y0, y0 = y1, y1 = t;

has this anything to do with comma operator , in the sense of returning/assigning the last value, or equivalent to

if (y1 < y0) {
  t = y0;
  y0 = y1;
  y1 = t;
}

I was more worried about, anything tricky happening here by relying on the order of operation.

Answer 1

Yes, the first snippet uses the comma operator and both snippets are equivalent, as the comma operator evaluates from left to right.

The comma operator is used in your snippet to put multiple assignments into a single statement , so they are all governed by the preceding if and a few characters ( { and } ) can be saved.

Not sure if this is worth doing manually, but minifiers typically do this kind of optimization (and it adds up)