JavaScript String substring()

substring() returns part of a string between a start index and an optional end index. The start is included and the end is excluded.

const text = "Welcome to plus2net.com";
console.log(text.substring(11, 19)); // plus2net

substring() Syntax Top ↑

string.substring(indexStart)
string.substring(indexStart, indexEnd)

Extract from One Index to the End Top ↑

const text = "JavaScript";
console.log(text.substring(4)); // Script

Extract Between Start and End Indexes Top ↑

The end index itself is not included.

const text = "JavaScript";
console.log(text.substring(0, 4)); // Java

If Start Is Greater Than End, substring() Swaps Them Top ↑

const text = "JavaScript";
console.log(text.substring(4, 0)); // Java

This is different from slice(4, 0), which returns an empty string.

Negative Values Are Treated as 0 Top ↑

const text = "JavaScript";
console.log(text.substring(-3, 4)); // Java

substring() vs slice() Top ↑

slice() supports negative indexes that count from the end and does not swap reversed arguments. substring() clamps negative values to 0 and swaps start/end when necessary.

substring() vs Legacy substr() Top ↑

substr() uses start, length. substring() uses start, end. The similar names are a common source of mistakes.

Extract the Domain Label from an Email-Like String Top ↑

The original page combined indexOf() and substring(). This keeps the example but finds the dot after the @, which is safer than simply taking the first dot anywhere in the address.

const email = "userid@example.com";
const start = email.indexOf("@") + 1;
const end = email.indexOf(".", start);
const domainLabel = email.substring(start, end);
console.log(domainLabel); // example

For broader examples, see indexOf() and email string processing.

Common substring() Mistakes Top ↑

• Expecting the end index to be included.
• Confusing the second argument with a character count.
• Expecting negative indexes to count from the end.
• Forgetting that reversed arguments are swapped.
• Confusing substring() with legacy substr().

← String Reference indexOf() →

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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