[JavaScript] String startswith, endswith and contains Implementation

When we do programming with strings, it's very common to have the following questions:

how do I check whether the string starts with prefix?

how do I check whether the string ends with suffix?

how do I check whether the string contains sub-string?

We will show how to do these case by case in JavaScript:

String startswith

We can use JavaScript built-in indexOf() function to check whether a string starts (or begins) with prefix. For alternative solution, please refer to reference [1].

/**
 * The string starts with prefix?
 * @param {string} string The string starts with prefix?
 * @param {string} prefix The string starts with prefix?
 * @return {boolean} true if string starts with prefix, otherwise false
 */
startswith = function(string, prefix) {
  return string.indexOf(prefix) == 0;
};

String endswith

Again we use JavaScript built-in indexOf() function to check whether a string ends with suffix. For alternative solution, please refer to reference [2].

/**
 * The string ends with suffix?
 * @param {string} string The string ends with suffix?
 * @param {string} suffix The string ends with suffix?
 * @return {boolean} true if string ends with suffix, otherwise false
 */
endswith = function(string, suffix) {
  return string.indexOf(suffix, string.length - suffix.length) != -1;
};

String contains

The same trick of JavaScript built-in indexOf() function to check whether a string contains another string. For alternative solution, please refer to reference [3].

/**
 * The string contains substr?
 * @param {string} string The string contains substr?
 * @param {string} substr The string contains substr?
 * @return {boolean} true if string contains substr, otherwise false
 */
contains = function(string, substr) {
  return string.indexOf(substr) != -1;
};

References:

[1]	How to check if a string “StartsWith” another string?

[2]	endsWith in javascript

[3]	How can I check if one string contains another substring?

[4]	JavaScript String indexOf() Method

[5]	JavaScript basename()