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

Answer 1

when you use == or != in js,the operands will be converted to the same type before making the comparison.when converting:

if there is a Boolean, true will be turned to 1 and false turned to 0;

    var a = true;
    a == 1;// a turned to 1 before compare,so true
    a == 2;// a turned to 1 before compare,so false

Answer 2

This is to do with coercion. In the a == 1 scenario, a is coerced into a an integer to compare again 1, true is coerced to 1. In the second example, a is again coerced to 1, so it doesn't equal 2.

Further reading on coercion

Answer 3

Well because 0 = false and 1 = true. There are only two values for a boolean: true/false. So what should 2 be?

var has no type, it can be everything. Please consider also the == vs === operator.

var x = 1;
console.log(x === true);
console.log(x == true);
x = 2;
console.log(x === true);
console.log(x == true);
x = 0;
console.log(x === false);
console.log(x == false);
x = -1;

See the example: http://jsfiddle.net/2aqGS/146/

Answer 4

You may convert 1 to True and True to 1 but you can't convert other numerics to True.

Answer 5

That's probably inherited from binary world and it makes sense, because in binary 0 is false and 1 is true. Exactly, that is how type conversion been done for boolean types in javascript as well while comparing.

For boolean there are only 2 possibles, true or false. Hence in number/binary system 0 and 1 are apt to represent them.

Answer 6

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.