Types & Coercion interview questions

1. A.a historical bug where typeof returns 'object' for null
2. B.== coerces operands to a common type before comparing; === compares value and type with no coercion
3. C.a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it
4. D.the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy

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1. A.Falsy values
2. B.== vs ===
3. C.Primitive types
4. D.typeof null

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1. A.typeof null — the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint
2. B.typeof null — a unique immutable primitive, typically used as a non-colliding object property key
3. C.typeof null — a historical bug where typeof returns 'object' for null
4. D.typeof null — a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it

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1. A.the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy
2. B.the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint
3. C.a historical bug where typeof returns 'object' for null
4. D.a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it

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1. A.Falsy values
2. B.Symbol
3. C.== vs ===
4. D.Primitive types

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1. A.Primitive types — a unique immutable primitive, typically used as a non-colliding object property key
2. B.Primitive types — a historical bug where typeof returns 'object' for null
3. C.Primitive types — the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy
4. D.Primitive types — the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint

Answer + AI explanation with a free account

1. A.== coerces operands to a common type before comparing; === compares value and type with no coercion
2. B.a unique immutable primitive, typically used as a non-colliding object property key
3. C.a historical bug where typeof returns 'object' for null
4. D.the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy

Answer + AI explanation with a free account

1. A.typeof null
2. B.Falsy values
3. C.== vs ===
4. D.Primitive types

Answer + AI explanation with a free account

1. A.== vs === — a historical bug where typeof returns 'object' for null
2. B.== vs === — the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy
3. C.== vs === — a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it
4. D.== vs === — == coerces operands to a common type before comparing; === compares value and type with no coercion

Answer + AI explanation with a free account

1. A.a historical bug where typeof returns 'object' for null
2. B.the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy
3. C.the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint
4. D.a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it

Answer + AI explanation with a free account

1. A.NaN
2. B.typeof null
3. C.Falsy values
4. D.== vs ===

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1. A.NaN — a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it
2. B.NaN — the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint
3. C.NaN — a unique immutable primitive, typically used as a non-colliding object property key
4. D.NaN — == coerces operands to a common type before comparing; === compares value and type with no coercion

Answer + AI explanation with a free account

1. A.the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint
2. B.a historical bug where typeof returns 'object' for null
3. C.the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy
4. D.a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it

Answer + AI explanation with a free account

1. A.typeof null
2. B.== vs ===
3. C.Primitive types
4. D.Falsy values

Answer + AI explanation with a free account

1. A.Falsy values — the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy
2. B.Falsy values — == coerces operands to a common type before comparing; === compares value and type with no coercion
3. C.Falsy values — a historical bug where typeof returns 'object' for null
4. D.Falsy values — the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint

Answer + AI explanation with a free account

1. A.== coerces operands to a common type before comparing; === compares value and type with no coercion
2. B.a unique immutable primitive, typically used as a non-colliding object property key
3. C.a historical bug where typeof returns 'object' for null
4. D.the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy

Answer + AI explanation with a free account

1. A.Symbol
2. B.Falsy values
3. C.Primitive types
4. D.== vs ===

Answer + AI explanation with a free account

1. A.Symbol — a numeric value meaning 'not a number'; NaN !== NaN, so Number.isNaN is used to test for it
2. B.Symbol — a unique immutable primitive, typically used as a non-colliding object property key
3. C.Symbol — the 7 immutable value types: string, number, boolean, null, undefined, symbol, bigint
4. D.Symbol — the values false, 0, '', null, undefined, NaN and 0n — everything else is truthy

Answer + AI explanation with a free account