Rules to keep in mind while using if statement in javascript

Evaluation of different data types in javascript

• Objects evaluate to true
• Undefined evaluates to false
• Null evaluates to false
• Booleans evaluate to the value of the boolean
• Numbers evaluate to false if +0, -0, or NaN, otherwise true
• Strings evaluate to false if an empty string '', otherwise true
• Arrays (whether empty or not ex: [] or [0]) evaluates to true as array is an object

Prefer strict comparison over loose comparison

It is better to use strict comparison(===) over loose comparison(==) as the strict comparison does not do any coercion.

Coercion: Coercion in javascript refers to the process of automatic or implicit conversion of values from one data type to another.

References

Airbnb style guide
Comparison in javascript