Javascript强制示例中需要澄清

Question

var a = 1+1+'2';
console.log(a);
> 22

var a = 1+1+'2'+7;
console.log(a);
> 227

var a = 1+1+'2'+7+10;
console.log(a);
> 22710

var a = 1+1+'2'+7+10-2;
console.log(a);
> 22708

where is the 0 coming from in 22708? coercion example.

Answer 1

The hint is in the previous evaluation. 1+1+'2'+7+10-2 is equivalent to ((1+1)+'2'+7+10)-2 , or "22710"-2 . While + is defined for both strings and numbers (it's addition when both arguments are numbers, concatenation in any other case), - is only defined for numbers; and so "22710" is coerced to number: 22710-2 is indeed 22708 .

Answer 2

Javascript handles the subtract and minus signs differently. You get the zero because it is taking 22710 and subtracting 2 to get 22708 .

So it goes from 2 To 22 To 227 To 22710 To 22710 - 2 Which gives 22708

The actual reason as to why is way over my head though.