Angular - State Management
You want to create a signal that holds a list of numbers and add a new number to it reactively. Which code correctly updates the signal to add number 7?
You want to create a signal that holds a list of numbers and add a new number to it reactively. Which code correctly updates the signal to add number 7?
hard📝 component behavior Q15 of 15
Step-by-Step Solution
Solution:
Step 1: Understand how to update array signals
Signals hold values immutably; to add an item, create a new array with the old items plus the new one.Step 2: Check each option's correctness
numbers.update(list => [...list, 7]); usesupdate()with a function that returns a new array including 7, which is correct.
numbers.set(numbers() + 7); tries to add 7 to an array directly, causing a type error.
numbers = signal([...numbers(), 7]); tries to reassign the signal variable, which is incorrect.
numbers.push(7); callspush()on the signal itself, which is not valid.Final Answer:
numbers.update(list => [...list, 7]); -> Option DQuick Check:
Use update() with function returning new array [OK]
Quick Trick: Use update(fn) to immutably add items to array signals [OK]
Common Mistakes:
- Trying to mutate signal value directly
- Reassigning signal variable instead of updating
- Using set() with wrong value type
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