padStart and trim

Learn string formatting with .padStart and .trim.

Padding with padStart

To pad a string to a specific length you use .padStart(targetLength, padString). The string is prefixed with padString until the target length is reached. "5".padStart(3, "0") returns "005".

padStart is useful for showing codes, phone or sequence numbers at a fixed width. For example "42".padStart(6, "0") returns "000042"; this way every code in a list lines up at the same width. Its counterpart .padEnd() pads at the end.

Trimming whitespace with trim

To remove leading and trailing whitespace (space, tab, newline) from a string you use .trim(). " alex ".trim() returns "alex". Whitespace often appears around user input; trim removes it in one call.

To remove only leading whitespace use .trimStart(), only trailing use .trimEnd(). trim does not modify the original string; it returns a new one. Trimming fields like email or username makes comparisons reliable.

Exercise Pad the code to 6 characters

The code variable holds "42". Declare a variable padded and assign the result of code.padStart(6, "0") to it. Then print padded with console.log. The output on a single line must be 000042.

Show example solution

const code = "42";
const padded = code.padStart(6, "0");
console.log(padded);

Test yourself

Write the padStart call

const code = "5";
const padded = code____(3, "0");

Show answer

const code = "5";
const padded = code.padStart(3, "0");

What is the result of "7".padStart(4, "0")?
```
"7".padStart(4, "0")
```
- "7"
- "7000"
- "0007"
- "0"
Show answer

"0007" — padStart(4, "0") prepends three zeros; the result is "0007".
Match each method to its job

.padStart(n, x)

Pads at the start
.padEnd(n, x)

Pads at the end
.trim()

Removes side whitespace
.trimStart()

Removes only the start

Next lesson: Summary - Strings

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