When would JavaScript == make more sense than ===?
As Which equals operator (== vs ===) should be used in JavaScript comparisons? indicates they are basically identical except ' === ' also ensures type equality and hence ' == ' might perform type conversion. In Douglas Crockford's JavaScript: The Good Parts, it is advised to always avoid ' == '. However, I'm wondering what the original thought of designing two set of equality operators was.
Have you seen any situation that using ' == ' actually is more suitable than using ' === '?
Consider a situation when you compare numbers or strings:
if (4 === 4)
{
// true
}
but
if (4 == "4")
{
// true
}
and
if (4 === "4")
{
// false
}
This applies to objects as well as arrays.
So in above cases, you have to make sensible choice whether to use == or ===
The simple answer is that '==' makes more sense than '===' when you want type coercion to happen during comparisons.
A good example would be numbers being passed in a URL query string. If for instance you have paginated content, and the page query parameter holds the current page number, then you could check for the current page with if (page == 1) ... even though page is actually "1" , not 1 .
I would suggest that there is no problem with using == , but to understand when and why to use it (ie use === as a rule, and == when it serves a purpose). Essentially, == just gives you shorthand notation - instead of doing something like
if (vble === 0 || vble === "" || vble === null || vble === undefined || vble === false) ...
It's much easier to just write
if (vble == false) ...
(Or even easier to write)
if (!vble) ...
Of course there are more examples than just looking for "truthy" or "falsey" values.
Really, you just need to understand when and why to use == and === , I don't see any reason why not to use == where it fits better...
Another example is using this shorthand to allow shorthand method calls:
function func(boolOptionNotCommonlyUsed) {
if (boolOptionNotCommonlyUsed) { //equiv to boolOptionNotCommonlyUsed == true
//do something we rarely do
}
//do whatever func usually does
}
func(); //we rarely use boolOptionNotCommonlyUsed, so allow calling without "false" as an arg