if var a = true then a == 1 is true but a == 2 is false. Why? [duplicate]

Answer 1

Why? I understand that in javascript boolean expressions 0 casts to false and 1 casts to true.

Because Number(true) => 1

As per spec of abstract equality expression evaluation

8. If Type(x) is Boolean, return the result of the comparison ToNumber(x) == y.

Hence a is first coerced into a Number and then compared with 1.