why is == considered ALWAYS a bad practice in JavaScript [closed]

Question

I know that there are many quirks with the equality operator (==). For example, following are all true...

null == undefined
1 == '1'
true == 1
false == ''

In all the above cases, using identity operator (===) would have returned the (strictly) correct answer.

But, when I just want to compare simpler things that do not suffer from quirks, why shouldn't I use the equality operator. For example...

typeof x == 'number'
str == 'something'

So, my question is; why does the equality operator have such a derogatory status, when in fact it's useful in some situations.

Answer 1

It is considered bad because of something called type coercion.

It means that "" == false is true in JavaScript, but "" === false is not.

That might be what you want, but might not be.

Saying this is ALWAYS bad practice is too much of a sweeping statement. It is bad if you don't know what it does and means.

Answer 2

There is absolutely nothing wrong with using == when the operands are guaranteed to be of the same type. When the operands are of the same type, it is specified to perform exactly the same steps as ===. A good example is when using typeof.

The reason for == being frowned upon in such circumstances is purely stylistic. The argument is that code is easier to read if === is used consistently throughout without having to consider the implications of seeing a use of ==. A lot of this originates with Douglas Crockford and is perpetuated by his JSLint tool.