LIKE in JavaScript

LIKE is commonly used in SQL for matching strings that contain certain substrings.

For example, this code will match all users who’s name contains john:

SELECT * FROM users WHERE name LIKE '%john%';
Code language: JavaScript (javascript)

A similar thing can be done in JavaScript by using this contains function:

function contains(str, search, caseInsensitive = false) {
  if (typeof str !== 'string') {
    str = String(str);
  }

  if (caseInsensitive) {
    str = str.toLowerCase();
    search = search.toLowerCase();
  }

  return str.indexOf(search) !== -1;
}
Code language: JavaScript (javascript)

The contains function will automatically cast the provided str to a string if it is not already a string. Then, the function uses the indexOf method to check if the str string contains the search string. If it does, the function returns true, otherwise it returns false.

LIKE is case-sensitive or case-insensitive depending on the individual database engine used. For example, MySQL is usually case-insensitive and Postgres is case-sensitive.

As such, the above function is optionally case-sensitive or not and that can be controlled with the third parameter. By default the search is case-sensitive. If true is specified then the search will be done case-insensitive.

contains("Hello, World!", "world");  // returns false
contains("Hello, World!", "WORLD", true);  // returns true
Code language: JavaScript (javascript)

Another way to check if a string contains a substring is to use the String.protoype.includes() method:

"Hello, World!".includes("world") // returns false
"Hello, World!".toLowerCase().includes("world") // returns true
Code language: JavaScript (javascript)