Question

I am using lint and for the following:

if (json.RowKey != json.NewRowKey)

It gives me a message:

Expected '!==' and instead saw '!='.

Can someone explain what this means?

Answer 1

== will attempt to convert the types of the two operands to be the same before comparing them. Thus "2" == 2 is true.

=== will not attempt to convert the types of the two operands so if they are not the same type, they will never be ===. Thus "2" === 2 is false.

It is better to use === and !== as your default choice and only use == or != when you explicitly want to allow type conversion. If you are not expecting the two operands to be different types, then === and !== is more likely to do what you are expecting.

This avoids coding mistakes when things are not really equal and your code doesn’t intend for them to be equal.

Some odd things that happen with == (and do not happen with ===) that you may not expect and can lead to trouble. All of these evaluate to true:

null == undefined
false == '0' 
0 == '0' 
0 == ''

There’s more detail written here: Which equals operator (== vs ===) should be used in JavaScript comparisons?