Arrays store indexed elements and expose operations for reading, replacing and transforming values. An index can be absent; account for that in your logic.
Before you begin
Know basic HTML and simple JavaScript expressions. Choose a browser or server runtime deliberately and record how the example is run.
Work through the idea
Make the state, input and expected result explicit before changing the interface. Check the calculation separately from the event handler. Use fictional data and inspect an invalid input as well as a normal one. A visible result should correspond to a completed operation, not merely to a clicked button.
- Read by index
- Check boundaries
- Distinguish in-place mutation from a new result
Practice task
Replace the second item in a fictional shopping list and create a separate filtered list.
Check your result
Explain the original list, changed list and an out-of-range lookup.
A mistake to avoid
Do not assume that assigning one array variable to another copies the array.
Keep a review note
Save the inputs or scenario, your reasoning and the result you checked. Explain one assumption and one case that needs more work. Revise the exercise after feedback and distinguish what you demonstrated from what remains untested.
Official reference for further study
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