Can someone explain why the following code only works when I put beerCount-1 in parentheses? I'm really confused.
var beerCount = 99
function beer(){
while (beerCount>0) {
console.log(beerCount + " of beer on the wall. " + beerCount + " of beer. Take one down, pass it around, " + (beerCount-1) + " of beers on the wall.");
beerCount--;
}
}
beer()+ and - have the same operator precedence: 14, and they both evaluate left-to-right.
When a string is +d with anything else, the resulting operation is concatenation: the other side, if it isn't a string, is coerced with a string. (If both sides are numbers, the resulting operation is addition)
But only numbers can be -d from each other. If something on one side of the - can't be coerced to a number, NaN will be the result.
So, with
"someString " + (beerCount-1) + " someOtherString"
The parentheses ensure that the middle expression gets evaluated first:
"someString " + someNumber + " someOtherString"
Without it, due to left-to-right operations, you get:
"someString " + beerCount - 1 + " someOtherString"
// ^^^^^^^^^^^^^^^^^^^^^^ evaluate first
"someString 99" - 1 + " someOtherString"
// ^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluate second, but cannot subtract;
// "someString 99" cannot be coerced to a number, so result is NaN
NaN + " someOtherString"
which doesn't work.
