== vs === and type coercion

• Try the comparisons in the browser console and look for the one that breaks transitivity.

Model answer. Type coercion is JavaScript converting a value to another type automatically, for example '5' * 2 gives 10 (string to number), and '5' + 2 gives '52' (number to string, because + with a string concatenates).

• === (strict equality) compares type and value with no conversion: 5 === '5' is false.
• == (loose equality) first coerces the operands to a common type, following a long rule table: 5 == '5' is true.

Loose equality produces results that are easy to misread:

0 == ''          // true
0 == '0'         // true
'' == '0'        // false (not transitive!)
null == 0        // false
null == undefined // true
[] == false      // true

Because of these, use === and !== by default; convert explicitly when you mean to (Number(input) === 5). The one common, deliberate use of == is x == null, which is true for both null and undefined.