javascript - JSLint Expected '===' and instead saw '=='

Question

Recently I was running some of my code through JSLint when I came up with this error. The thing I think is funny about this error though is that it automatically assumes that all == should be ===.

Does that really make any sense? I could see a lot of instances that you would not want to compare type, and I am worried that this could actually cause problems.

The word "Expected" would imply that this should be done EVERY time.....That is what does not make sense to me.

Answer 1

IMO, blindly using ===, without trying to understand how type conversion works doesn't make much sense.

The primary fear about the Equals operator == is that the comparison rules depending on the types compared can make the operator non-transitive, for example, if:

A == B AND
B == C

Doesn't really guarantees that:

A == C

For example:

'0' == 0;   // true
 0  == '';  // true
'0' == '';  // false

The Strict Equals operator === is not really necessary when you compare values of the same type, the most common example:

if (typeof foo == "function") {
  //..
}

We compare the result of the typeof operator, which is always a string, with a string literal...

Or when you know the type coercion rules, for example, check if something is null or undefinedsomething:

if (foo == null) {
  // foo is null or undefined
}

// Vs. the following non-sense version:

if (foo === null || typeof foo === "undefined") {
  // foo is null or undefined
}