4.1.2 JS String Search

JavaScript String lastIndexOf()

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

Example

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

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

Example

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

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

Example

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

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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.

Example

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

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JavaScript String search()

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

Example

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

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

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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).

Examples

Perform a search for "ain":

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

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Perform a search for "ain":

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

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Perform a global search for "ain":

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

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Perform a global, case-insensitive search for "ain":

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

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JavaScript String matchAll()

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

Example

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

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

Example

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

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

Example

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

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JavaScript String includes()

• The includes() method returns true if a string contains a specified value.
• Otherwise it returns false.

Examples

Check if a string includes "world":

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

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

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

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JavaScript String startsWith()

• The startsWith() method returns true if a string begins with a specified value.
• Otherwise it returns false:

Examples

Returns true:

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

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Returns false:

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

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A start position for the search can be specified:

Returns false:

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

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Returns true:

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

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JavaScript String endsWith()

• The endsWith() method returns true if a string ends with a specified value.
• Otherwise it returns false:

Examples

Check if a string ends with "Doe":

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

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

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

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