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Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge The correct constructor signature for CustomEvent is:
new CustomEvent(eventName, optionsObject)
Where:
eventName is a string.
optionsObject may include:
detail → used to pass custom data
bubbles
cancelable, etc.
Example:
new CustomEvent('update', {
detail: { recordId: '123abc' }
});
Now evaluate each option:
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Option A
{ type: 'update', recordId: '123abc' }
Incorrect: The constructor requires (eventName, options), not a single object. type is not used this way.
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Option B
'update', { detail: { recordId: '123abc' } }
Correct format. detail is the proper place for custom event data.
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Option C
'update', '123abc'
Incorrect: The second argument must be an object (options), not a string.
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Option D
'update', { recordId: '123abc' }
Acceptable because any extra properties on the options object are still allowed, even though best practice is to use detail.
This still creates a valid CustomEvent, and the event will dispatch successfully.
Thus the two correct answers are B and D.
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JavaScript Knowledge Reference (text-only)
new CustomEvent(name, options) is the required syntax.
The detail property of the options object is the standard location for custom data.
The second argument must be an object; other types are invalid.