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javascriptcoerciontype-coercion

implicit coercion in javascript

I am revisiting implicit coercion in javascript and realized that I have overlooked something and need clarification on it.

if 

var a = "5";
var b = 5;

and a==b will return true.

But there are two possible ways a==b could give true coercion right? It's either 5 == 5, or '5' == '5'. So which one is actually happening for the above example here?

Solution

  • The answer is in the Abstract Equality Comparison Algorithm in the spec, specifically:

    1. If Type(x) is String and Type(y) is Number, return the result of the comparison ! ToNumber(x) == y.

    (The ! before ToNumber(x) does not mean negation, it's a spec notation asserting that ToNumber(x) will never result in an abrupt termination.)

    It's a numeric comparison, "5" is converted to 5 and then the comparison is done.