JavaScript essentials check

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Question 1 of 14What does Number("26") return?

The number 26The string "26"The boolean true

Question 2 of 14What does [] === [] evaluate to?

true, because both arrays are emptyfalse, because they are different referencesundefined, because arrays cannot be compared

Question 3 of 14Which declaration should usually be preferred when a binding will not be reassigned?

constvarAn undeclared global variable

Question 4 of 14What does a JavaScript closure retain access to?

Bindings from the lexical scope where the function was createdOnly the function's parametersOnly global variables

Question 5 of 14How does an arrow function get its this value?

It inherits this from the surrounding lexical scopeIt always creates a new this valueIt always uses window as this

Question 6 of 14Which array method should you use to keep only items that match a condition?

filtermapfind when every matching item is needed

Question 7 of 14When immutably updating a nested object, what must be copied?

Each object level along the path that changesOnly the top-level object, even when nested objects changeNothing; direct mutation is equivalent

Question 8 of 14Which operator provides a fallback only when a value is null or undefined?

??||&&

Question 9 of 14Where are ordinary methods declared in a JavaScript class shared?

On the class prototypeAs a separate copied function on every instance automaticallyOn the global object

Question 10 of 14What is a key benefit of ES modules?

Imports and exports make dependencies explicitEvery variable automatically becomes globalAll files share one hidden scope

Question 11 of 14Where should an error usually be caught?

At a layer that can recover, report, retry, or translate the failureInside every function regardless of contextErrors should never be caught

Question 12 of 14How should two independent asynchronous requests usually be started together?

Pass both promises to Promise.allAwait the first before creating the secondCall both functions without observing their promises

Question 13 of 14What does an async function always return?

A promiseundefinedA generator object

Question 14 of 14Given synchronous code, a resolved Promise.then callback, and setTimeout(..., 0), which runs first after the synchronous code completes?

The Promise.then callbackThe setTimeout callbackEither one can run first randomly

Choose one answer for every question, then check your answers.