Step 3 / Select topic JavaScript Hard

What this bank covers

• An object return replaces the new instance
• A primitive return keeps the instance
• Field initializers run before the constructor body
• A later field can read an earlier field
• An earlier field reads a later field as undefined
• Derived fields initialize when super returns
• Static fields run during class evaluation
• The base class finishes before the subclass body
• A class constructor requires new
• new.target is the constructed subclass
• extends is evaluated before the class body
• extends null has no prototype parent
• Class methods are non-enumerable
• Symbol.hasInstance customizes instanceof
• bind reduces length by the bound arguments
• A bound function has no prototype property
• new Function does not close over locals
• new Function is sloppy unless the source is strict
• Strict arguments do not alias parameters
• Sloppy arguments alias the named parameter
• call(null) is not rewritten in strict mode
• Strict direct eval does not leak var
• A body let cannot reuse a parameter name
• A default cannot read a later parameter
• yield* yields values, then returns the inner result
• throw injects an exception at the paused yield
• return completes the generator and runs finally
• An async return adopts a thenable
• The promise executor runs synchronously
• A second resolve is ignored
• Promise.resolve returns a native promise unchanged
• Promise.resolve adopts a thenable
• A throwing then rejects the adopting promise
• A microtask queued inside then runs after queued jobs
• JSON.stringify writes -0 as 0
• JSON.stringify rejects bigint
• JSON.stringify rejects a cycle
• toJSON replaces the object being serialized
• A reviver sees children before the parent
• structuredClone preserves a cycle
• structuredClone keeps a Map as a Map
• A false set trap throws in strict mode
• A false deleteProperty trap throws in strict mode
• A get trap must honor a frozen data property
• Strict assignment to a non-writable property throws
• Strict assignment to a frozen object throws
• Strict delete on a sealed object throws
• Strict assignment cannot extend a non-extensible object
• Date addition concatenates and subtraction subtracts
• Ordinary ToPrimitive swaps order by hint
• Symbol.toStringTag sets the Object toString tag
• Unsigned right shift turns -1 into the uint32 max
• Bitwise OR truncates toward zero through int32
• Both sums collapse to the same float
• Dividing by negative zero yields -Infinity
• Math.round breaks ties toward +Infinity
• Array sort is stable
• Map treats +0 and -0 as one key
• with returns a new array
• findLast returns the last match
• reduce skips holes
• copyWithin copies from a snapshot of the overlap
• A typed array is not an Array
• Only a literal __proto__ key sets the prototype
• BigInt and Number cannot be mixed with +
• bigint has its own typeof and is not === to a number
• BigInt division truncates toward zero
• Unary plus cannot convert a symbol
• String concatenation rejects a symbol, String() does not
• A returned object does not receive the public fields
• Optional call skips the argument list
• Nullish assignment ignores 0
• Logical or assignment keeps a truthy left side
• The comma operator yields the right operand
• A bare arrow has no super binding
• A sticky regexp anchors at lastIndex
• Without u or v, \p is an identity escape
• A tagged illegal escape cooks to undefined
• toString tags null as Null
• Strict mode hides arguments.callee
• Indirect eval does not bind locals
• super reaches a base static method
• Symbol.species chooses the map constructor
• A module namespace object is not extensible
• Dynamic import fulfills with the namespace
• A finally throw replaces the pending exception
• Private names are branded per class
• A static block sees an earlier private static field
• Error cause is a separate property
• AggregateError keeps an errors array
• for await...of walks an async iterable in order
• An async generator stays paused at yield
• matchAll requires a global regexp
• Named groups live on match.groups
• toSpliced copies instead of mutating
• toReversed copies instead of mutating
• JSON.stringify skips symbol keys
• The get trap receiver is the proxy
• A has trap cannot hide a non-configurable property
• Public instance fields are enumerable
• Spread arguments are limited by the stack
• return await inside try/catch
• Run independent awaits concurrently
• Catastrophic backtracking