Does strict equality guarantees loose equality

Question

I'm starting to write unit tests for my nodeJS/Javascript app with Mocha.

For my equality assertions tests I decided to use

• assert.strictEqual to test for equality
• assert.notEqual to test for difference

The idea behind this is to enforce the use of the strict equality operator ( === and !== ) but to be sure no error will be produced if == and != are used.

But it led me to a question :

For every possible a does a === b means a == b and does a !== b means a != b ?

Answer 1

The === and !== ensure that no only are the items considered 'equal' but that they are the same type - no type coercion is done:

"1" == 1 //true
"1" === 1 //false

It's the same for the inequality operator:

"2" != 1 //true
"2" !== 1 //true

"1" != 1 //false
"1" !== 1 //true

So, short answer, "For every possible a does a == b means a === b and does a != b means a !== b ?" - No.

Answer 2

否。例如0 !== false却0 == false 。

Answer 3

The === comparison is stronger than == . A == comparison just checks if two values are equal, performing type conversions as needed. A === comparison check that both the type and the value are the same. So a === b implies a == b , and a != b implies a !== b .

Example:

"100" ==  100    ->  true
"100" === 100    ->  false
"100" !=  100    ->  false
"100" !== 100    ->  true