Explain the difference between `==` and `===`

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Re-explain

=== compares value and type with no conversion, while == converts both sides to a common type and then compares. That conversion is called type coercion.

With loose equality, 5 == "5" is true because the string becomes a number first. With strict equality, 5 === "5" is false because a number and a string are different types. A special case is null == undefined, which is true, while null === undefined is false.

The coercion rules are hard to predict, so use === by default. The one common exception is value == null, which checks for null and undefined together.

5 == "5";    // true (coercion)
5 === "5";   // false (different types)
null == undefined;  // true
null === undefined; // false

Rewriting in plainer words…

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Likely follow-ups

What conversion steps does == apply when one side is a boolean or an object? Booleans become numbers, objects go through ToPrimitive, then the comparison runs again. Show why "0" == false is true.
Why is NaN === NaN false, and what's the right way to test for NaN? NaN is unequal to everything, itself included. Use Number.isNaN or Object.is. The global isNaN converts to a number first, so isNaN("abc") is true.
How is Object.is different from ===? They differ in two cases only. Object.is(NaN, NaN) is true and Object.is(0, -0) is false.
Two objects have identical properties. Why does === return false, and how would you compare them? For objects, === compares references. Contrast a shallow key-by-key check with a recursive deep comparison.
Is there ever a good reason to write == in production code? value == null is the accepted case. Say the team rule allows only that and uses === everywhere else.

What you can say

Triple equals checks value and type with no conversion, while double equals converts both sides to a common type and then compares.
That conversion is called type coercion. It's why 5 == "5" is true, because the string turns into the number 5 first.
With triple equals, 5 === "5" is false, because a number and a string are different types.
One special case is null == undefined, which is true, while null === undefined is false.
The coercion rules are hard to predict, so I use triple equals by default.
The one exception I'd make is value == null, which checks for null and undefined in a single comparison.

Weak answers to avoid

Says == ignores type, never names coercion == doesn't ignore type. It converts the values first. Name type coercion and use 5 == "5" to show the mechanism.
Claims === compares object contents For objects, both operators compare references, so {} === {} is false. Miss this and the interviewer will doubt how well you know reference types.
Bans == outright with no exception It sounds like a linter rule repeated from memory. Mention value == null as the one common deliberate use and say what it catches.
Recites [] == ![] tricks without the rule Party tricks show memory, not understanding. Explain the conversion rule and why it makes === the safer default.

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