Learn JS #13

Posted on by Apostube

JavaScript String Search

JavaScript Search Methods

  • String indexOf()
  • String lastIndexOf()
  • String startsWith()
  • String endsWith()

JavaScript String indexOf()

The indexOf() method returns the index of (the position of) the first occurrence of a specified text in a string:

Example

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

Note:

  • JavaScript counts positions from zero.
  • 0 is the first position in a string, 1 is the second, 2 is the third, …

JavaScript String lastIndexOf()

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

Example

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

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

Example

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

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

Example

let str = "Please locate where 'locate' occurs!";
str.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.

Example

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

JavaScript String search()

The search() method searches a string for a specified value and returns the position of the match:

Example

let str = "Please locate where 'locate' occurs!";
str.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 searches a string for a match against a regular expression, and returns the matches, as an Array object.

Example 1

Search a string for “ain”:

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

Example 2

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 includes()

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

Example

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

Syntax

string.includes(searchvalue, start)
searchvalue Required. The string to search for
start Optional. Default 0. Position to start the search
Returns: Returns true if the string contains the value, otherwise false
JS Version: ES6 (2015)

Check if a string includes “world”, starting the search 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 false:

Example

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

text.startsWith("Hello");

Syntax

string.startsWith(searchvalue, start)

Parameter Values

Parameter Description
searchvalue Required. The value to search for.
start Optional. Default 0. The position to start the search.

Examples

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

text.startsWith("world")    // Returns false

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

text.startsWith("world", 5)    // Returns false

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

text.startsWith("world", 6)    // Returns true

Note: The startsWith() method is case sensitive.

JavaScript String endsWith()

The endsWith() method returns true if a string ends with a specified value, otherwise false:

Example

Check if a string ends with “Doe”:

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

Syntax

string.endsWith(searchvalue, length)

Parameter Values

Parameter Description
searchvalue Required. The value to search for.
length Optional. The length to search.

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

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

Note: The endsWith() method is case sensitive.

Apostube

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