String search

Learn to search with .indexOf, .includes and .startsWith.

Searching with indexOf

To find a substring's position you use the .indexOf() method. "hello world".indexOf("world") returns 6 because "world" starts at index 6. Indexing is zero-based.

If the substring is not found .indexOf() returns -1. This value is often used to check whether a substring exists: if (text.indexOf("@") !== -1) roughly tests whether a text might be an email.

includes and startsWith

.includes() returns true/false for whether a substring exists in a string: "welcome".includes("come") evaluates to true. It is a more readable form of .indexOf() !== -1.

.startsWith() tests whether a string begins with the given substring: "Mr. Smith".startsWith("Mr.") is true. Its counterpart .endsWith() checks the end. All three methods are case-sensitive.

Exercise Find and print the index

The sentence variable holds "Node.js rocks". Declare a variable pos and assign the result of sentence.indexOf("rocks") to it. Then print pos with console.log. The output on a single line must be 8.

Show example solution

const sentence = "Node.js rocks";
const pos = sentence.indexOf("rocks");
console.log(pos);

Test yourself

Match each method to its job

.indexOf(x)

Returns first index
.includes(x)

Asks whether it exists
.startsWith(x)

Checks the start
.length

Character count
What is the result of "notebook".includes("book")?
```
"notebook".includes("book")
```
- false
- -1
- 4
- true
Show answer

true — "book" is in "notebook"; includes returns true.

Write the startsWith call

const code = "US-CA";
const ok = code____("US-");

Show answer

const code = "US-CA";
const ok = code.startsWith("US-");

Next lesson: substring and slice

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