pos += 1 will increment the variable pos by 1, and return it.
pos = +1 is the same as saying pos = 1. The plus is redundant.
See it in action with this simple script:
pos1 = 10;
pos2 = 10;
pos1 += 1;
pos2 =+ 1;
console.log('pos1', pos1);
console.log('pos2', pos2);
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