Rendering a list

Read first Task 29

map the data, join optional, then set innerHTML once — one paint, fast.

Definition and example

Rendering a list is the focus of this lesson. map the data, join optional, then set innerHTML once — one paint, fast. The task asks you to apply that idea in a small example: How many innerHTML writes should a list render use. Before you run the code, predict what should happen. Then Inspect the browser output and the value your code produces and compare it with your prediction. If the result differs, change one relevant line and run it again. Testing one change at a time makes the cause of a result easier to understand.

JavaScript 1 automatic check The DOM

Code editor Ctrl + Enter runs

// TASK rendering-a-list-09: How many innerHTML writes should a list render use?
// STEPS: Read the explanation. Change one relevant line at a time, then run the code and compare the result with the check on the right.
const rows=[{t:'AI'},{t:'Py'}];
const html=rows.map(r=>`<li>${r.t}</li>`).join('');
document.body.innerHTML='<ul>'+html+'</ul>';
console.log(document.querySelectorAll('li').length);

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Checks on this task:

The output must include “2”.

The task and step-by-step instructions are written as comments at the top of the editor. Change one relevant line, run it, and compare the result with these checks.

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Rendering a list

Rendering a list

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