JavaScript basics · Lesson 4 of 12 · 10 minutes

JavaScript basics: Number calculations

Arithmetic operates on numbers. Converting units explicitly keeps an otherwise correct expression from answering the wrong question.

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1
Build number calculations
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
Arithmetic operates on numbers. Converting units explicitly keeps an otherwise correct expression from answering the wrong question.
The requested statements are present as code, not inside a string or comment. No arbitrary JavaScript is executed.
```
const seconds = 2;
```
Common mistake to avoid: A string containing code executes automatically when it is assigned.
2
Extend the number calculations 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
Arithmetic operates on numbers. Converting units explicitly keeps an otherwise correct expression from answering the wrong question.
The requested statements are present as code, not inside a string or comment. No arbitrary JavaScript is executed.
```
const seconds = 2;
const milliseconds = seconds * 1000;
```
Common mistake to avoid: A successful element lookup guarantees that the rest of an event handler is correct.
3
Verify the complete number calculations 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
Arithmetic operates on numbers. Converting units explicitly keeps an otherwise correct expression from answering the wrong question.
The requested statements are present as code, not inside a string or comment. No arbitrary JavaScript is executed.
```
const seconds = 2;
const milliseconds = seconds * 1000;
const perRequest = milliseconds / 4;
```
Common mistake to avoid: A string containing code executes automatically when it is assigned.

Understand the pattern

Arithmetic operates on numbers. Converting units explicitly keeps an otherwise correct expression from answering the wrong question.

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 seconds = 2;
const milliseconds = seconds * 1000;
const perRequest = milliseconds / 4;

Arithmetic operates on numbers. Converting units explicitly keeps an otherwise correct expression from answering the wrong question.

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 number calculations?A successful element lookup guarantees that the rest of an event handler is correct.Arithmetic operates on numbers. Converting units explicitly keeps an otherwise correct expression from answering the wrong question.A string containing code executes automatically when it is assigned.

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

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