DOM and events · Lesson 3 of 10 · 7 minutes

DOM and events: Click listeners

An event listener registers behavior for a future event; pass a function rather than its return value.

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Your objectives

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1
Build click listeners
Build this first target: the JavaScript statements shown in the example, as executable-position code rather than a string or comment. Explain how the values and control flow implement this lesson’s concept; this browser lab checks structure without executing arbitrary JavaScript.
Hint & worked example
An event listener registers behavior for a future event; pass a function rather than its return value.
The requested statements are present as code, not inside a string or comment. No arbitrary JavaScript is executed.
```
const button = document.querySelector("#start");
```
Common mistake to avoid: A string containing code executes automatically when it is assigned.
2
Extend the click listeners example
Extend your file to include: the JavaScript statements shown in the example, as executable-position code rather than a string or comment. Explain how the values and control flow implement this lesson’s concept; this browser lab checks structure without executing arbitrary JavaScript.
Hint & worked example
An event listener registers behavior for a future event; pass a function rather than its return value.
The requested statements are present as code, not inside a string or comment. No arbitrary JavaScript is executed.
```
const button = document.querySelector("#start");
function start() { button.textContent = "Practice started"; }
```
Common mistake to avoid: A successful element lookup guarantees that the rest of an event handler is correct.
3
Verify the complete click listeners pattern
Finish the pattern with: the JavaScript statements shown in the example, as executable-position code rather than a string or comment. Explain how the values and control flow implement this lesson’s concept; this browser lab checks structure without executing arbitrary JavaScript.
Hint & worked example
An event listener registers behavior for a future event; pass a function rather than its return value.
The requested statements are present as code, not inside a string or comment. No arbitrary JavaScript is executed.
```
const button = document.querySelector("#start");
function start() { button.textContent = "Practice started"; }
if (button) { button.addEventListener("click", start); }
```
Common mistake to avoid: A string containing code executes automatically when it is assigned.

Understand the pattern

An event listener registers behavior for a future event; pass a function rather than its return value.

Misconceptions to reject

A string containing code executes automatically when it is assigned.
A successful element lookup guarantees that the rest of an event handler is correct.

This is a code-inspection lab, not a full JavaScript runtime.

Worked example and expected result

const button = document.querySelector("#start");
function start() { button.textContent = "Practice started"; }
if (button) { button.addEventListener("click", start); }

An event listener registers behavior for a future event; pass a function rather than its return value.

Try a variation

Adapt the final example to a different project name while retaining its structure and relationships. A different context still needs a real browser and accessibility check.

Explain it

Which statement correctly explains click listeners?An event listener registers behavior for a future event; pass a function rather than its return value.A string containing code executes automatically when it is assigned.A successful element lookup guarantees that the rest of an event handler is correct.

Apply it elsewhere

You reuse click listeners in a different project. What must still be verified?Nothing; passing a single exercise guarantees every future use.Only whether the source code has the same number of lines.The input values, element availability, and actual behavior in a real browser.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

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