JavaScript String Search

JavaScript String indexOf()

The indexOf() method returns the index (position) of the first occurrence of a string in a string, or it returns -1 if the string is not found:

let text = "Please locate where 'locate' occurs!";
let index = text.indexOf("locate");

JavaScript String lastIndexOf()

The lastIndexOf() method returns the index of the last occurrence of a specified text in a string:

Both indexOf(), and lastIndexOf() return -1 if the text is not found:

let text = "Please locate where 'locate' occurs!";
let index = text.lastIndexOf("John");

Both methods accept a second parameter as the starting position for the search:

let text = "Please locate where 'locate' occurs!";
let index = text.indexOf("locate", 15);

The lastIndexOf() methods searches backwards (from the end to the beginning), meaning: if the second parameter is 15, the search starts at position 15, and searches to the beginning of the string.

let text = "Please locate where 'locate' occurs!";
text.lastIndexOf("locate", 15);

JavaScript String search()

The search() method searches a string for a string (or a regular expression) and returns the position of the match:

let text = "Please locate where 'locate' occurs!";
text.search("locate");
let text = "Please locate where 'locate' occurs!";
text.search(/locate/);

Did You Notice?

The two methods, indexOf() and search(), are equal?

They accept the same arguments (parameters), and return the same value?

The two methods are NOT equal. These are the differences:

• The search() method cannot take a second start position argument.
• The indexOf() method cannot take powerful search values (regular expressions).

You will learn more about regular expressions in a later chapter

JavaScript String match()

The match() method returns an array containing the results of matching a string against a string (or a regular expression).

let text = "The rain in SPAIN stays mainly in the plain";
text.match("ain");

Perform a search for “ain “:

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/);

Perform a global search for “ain” :

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/g);

Perform a global, case-insensitive search for “ain” :

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/gi);

JavaScript String matchAll()

The matchAll() method returns an iterator containing the results of matching a string against a string (or a regular expression).

const iterator = text.matchAll("Cats");

If the parameter is a regular expression, the global flag (g) must be set, otherwise a TypeError is thrown.

const iterator = text.matchAll(/Cats/g);

If you want to search case insensitive, the insensitive flag (i) must be set:

const iterator = text.matchAll(/Cats/gi);

JavaScript String includes()

The includes() method returns true if a string contains a specified value.

Otherwise it returns false.

let text = "Hello world, welcome to the universe.";
text.includes("world");

Check if a string includes “world”. Start at position 12:

let text = "Hello world, welcome to the universe.";
text.includes("world", 12);

JavaScript String startsWith()

The startsWith() method returns true if a string begins with a specified value.

Otherwise it returns false:

let text = "Hello world, welcome to the universe.";
text.startsWith("Hello");

Returns false :

let text = "Hello world, welcome to the universe.";
text.startsWith("world")

A start position for the search can be specified:

let text = "Hello world, welcome to the universe.";
text.startsWith("world", 5)

Returns true:

let text = "Hello world, welcome to the universe.";
text.startsWith("world", 6)

JavaScript String endsWith()

The endsWith() method returns true if a string ends with a specified value.

Otherwise it returns false:

let text = "John Doe";
text.endsWith("Doe");

Check if the 11 first characters of a string ends with “world”:

let text = "Hello world, welcome to the universe.";
text.endsWith("world", 11);