In Node.js, the Assert module provides two distinct modes for performing assertions: strict mode and legacy mode. Each mode has its own set of behaviors and use cases, particularly in how they handle equality comparisons.
Strict Mode
Strict mode in the Assert module enforces strict equality comparisons. This means that when comparing values, the module uses the === operator, which checks both the value and the type of the variables being compared. This mode is designed to avoid common pitfalls in JavaScript comparisons that can lead to unexpected results.
For example, in strict mode, assert.strictEqual(5, '5') would throw an assertion error because the number 5 is not strictly equal to the string '5' due to the type difference[3][4][6][9].
Strict mode also includes methods like assert.deepStrictEqual(), which performs a deep equality comparison, checking that the contents of objects are identical in terms of both structure and data type[3][4][6].
Legacy Mode
Legacy mode, on the other hand, uses loose equality comparisons (==), which convert the operands to the same type before making the comparison. This can lead to true evaluations in cases where the operands are not strictly the same, which might not be the desired behavior in testing scenarios.
For instance, assert.equal(5, '5') would pass in legacy mode because JavaScript coerces the string '5' to the number 5 before comparison, considering them equal[9][10].
Legacy mode includes methods like assert.deepEqual(), which checks objects for equality in a more lenient manner compared to assert.deepStrictEqual(). It does not require properties to have the same type, as long as they are loosely equal[9].
Key Differences and Recommendations
Type Coercion:
Strict Mode: No type coercion; values must be of the same type.
