## String Functions Studio provides a set of functions for working with strings in expressions. | Function | Arguments Description | | --- | --- | | [`substring()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#substring) | Extracts a specified substring from a given string. | | [`startsWith()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#startswith) | Determines whether a string begins with specific characters. | | [`endsWith()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#endswith) | Determines whether a string ends with specific characters. | | [`stringLength()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#stringlength) | Determines the number of characters in the specified string. | | [`indexOf()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#indexof) | Determines the index of the first occurrence of a substring. | | [`lastIndexOf()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#lastindexof) | Determines the index of the last occurrence of the specified value, searching backward. | | [`toUpperCase()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#touppercase) | Convert all characters in a string to upper case. | | [`toLowerCase()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#tolowercase) | Convert all characters in a string to lower case. | | [`replace()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#replace) | Replaces substrings within a string. | | [`contains()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#contains) | Determines whether one string may be found within another string. | | [`charAt()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#charat) | Get a new string containing the single character unit located at the specified offset. | | [`padStart()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#padstart) | Pads the front of the input string with another string until the resulting string reaches the given length. | | [`padEnd()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#padend) | Pads the end of the input string with another string until the resulting string reaches the given length. | | [`trim()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#trim) | Removes whitespace from both ends of a string. | | [`trimStart()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#trimstart) | Removes whitespace from the start of a string. | | [`trimEnd()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#trimend) | Removes whitespace from the end of a string. | | [`matches()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#matches) | Returns true for strings that match the provided regex. | | [`firstMatch()`](https://docs.foursquare.com/analytics-products/docs/expressions-string#firstmatch) | Returns the first string that matches given the provided regex. | ### Remarks - All indices into strings are zero-based, meaning that the first character has index `0`, not `1`. ## API Reference ### substring Extracts a specified substring from a given string. TypeScript ```typescript substring(string: string, startIndex: integer, endIndex?: integer): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The string to extract a substring from. | | `startIndex` | `int` | The index of the first character to be included. | | `endIndex` | `int` | The index of the first character to be excluded. If omitted, all characters to the end of the string are included. | #### Returns Returns a new string containing the specified part of the given string. #### Notes - If startIndex is equal to `endIndex`, `substring()` returns an empty string. - If `startIndex` is greater than `endIndex`, the effect of `substring()` is as if the two arguments were swapped. ### startsWith Determines whether a string begins with the characters of another string. TypeScript ```typescript startsWith(string: string, searchString: string, startIndex: integer): boolean ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The string to extract a substring from. | | `searchString` | `string` | The substring to look for. | | `startIndex` | `int` | The index of the first character to be included. | #### Returns Returns `true` or `false` as appropriate. #### Notes This method is case-sensitive. ### endsWith Determines whether a string ends with the characters of a specified string. TypeScript ```typescript endsWith(string: string, searchString: string, fromIndex?: integer): boolean ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The string to extract a substring from. | | `searchString` | `string` | The substring to check for. | | `fromIndex` | `int` | The index of the last character to be included. Defaults to the end of the string. | #### Returns Returns `true` or `false` as appropriate. #### Notes This method is case-sensitive. ### stringLength Determines the number of characters in the specified string. TypeScript ```typescript stringLength(string: string): integer ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The string to check for length. | #### Returns Returns the number of characters in the given string. ### indexOf Determines the index of the first occurrence of a substring. TypeScript ```typescript indexOf(string: string, substring: string, startIndex?: integer): integer ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The string to find a substring in. | | `substring` | `string` | The string to check for. | | `fromIndex` | `int` | The index to search backward from. Defaults to end of string. | #### Returns Returns the index of the first occurrence of `substring`; -1 if not found. ### lastIndexOf Determines the index of the last occurrence of the specified value, searching backward. TypeScript ```typescript lastIndexOf(string: string, searchString: string, fromIndex?: integer): integer ``` #### Returns Returns the index of the last occurrence of `substring`; -1 if not found. ### toUpperCase Convert all characters in a string to upper case. TypeScript ```typescript toUpperCase(string: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string to convert to upper case. | #### Returns Returns a new `string` with all lower case characters replaced with upper case characters. #### Notes The specifics of case conversion may depend on the current locale, determined by the browser and the operating system. ### toLowerCase Convert all characters in a string to lower case. TypeScript ```typescript toLowerCase(string: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string to convert to lower case. | #### Returns Returns a new `string` with all upper case characters replaced with lower case characters. #### Notes The specifics of case conversion may depend on the current locale, determined by the browser and the operating system. ### replace Replaces substrings within a string. TypeScript ```typescript replace(string: string, searchString: string, newSubstring: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string containing a substring to be replaced. | | `searchString` | `string` | The substring to be replaced. | | `newSubstring` | `string` | The replacement string. | #### Returns Returns a string with the replaced substring, or an unaltered string if no `searchString` was found. ### contains Determines whether one string may be found within another string. TypeScript ```typescript contains(string: string, searchString: string): boolean ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string to evaluate for a substring. | | `searchString` | `string` | The substring to search for. | #### Returns Returns `true` if the `searchString` is found inside the supplied string, otherwise `false`. ### charAt Get a new string consisting of the single character unit located at a specified offset. TypeScript ```typescript charAt(string: string, index: integer): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string. | | `index` | `int` | The index of the character. | #### Returns Returns a string containing the character at `index` at the specified index. If `index` is out of range, an empty string is returned. ### padStart Pads the front of the input string with another string until the resulting string reaches the given length. TypeScript ```typescript padStart(string: string, targetLength: integer, padString?: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string. | | `targetLength` | `int` | The minimum length of the returned string. | | `padString` | `string` | Optional. Applied (multiple times, if needed) from the start of the current string. Defaults to `' '` (Unicode Character U+0020 'SPACE'). | #### Returns Returns a string that has at least `targetLength` characters. ### padEnd Pads the end of the input string with another string until the resulting string reaches the given length. TypeScript ```typescript padEnd(string: string, targetLength: integer, padString?: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string. | | `targetLength` | `int` | The minimum length of the returned string. | | `padString` | `string` | Optional. Applied (multiple times, if needed) from the end of the current string. Defaults to `' '` (Unicode Character U+0020 'SPACE'). | #### Returns Returns a string that has at least `targetLength` characters. ### trim Removes whitespace from both ends of a string. TypeScript ```typescript trim(string: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string. | #### Returns Returns a string without leading and trailing whitespace. ### trimStart Removes whitespace from the start of a string. TypeScript ```typescript trimStart(string: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string. | #### Returns Returns a string with leading whitespace stripped. ### trimEnd Removes whitespace from the end of a string. TypeScript ```typescript trimEnd(string: string): string ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string. | #### Returns Returns a string with trailing whitespace stripped. ### matches Determines whether a string matches the provided regex. TypeScript ```typescript matches(string: string, regex: string): boolean ``` | Parameter | Type | Description | | --- | --- | --- | | `string` | `string` | The input string. | | `regex` | `string` | The regex argument to use in a search. | #### Returns Returns `true` if a string matches the provided regex, `false` otherwise. ### firstMatch Finds the first string that matches the provided regex. TypeScript ```typescript firstMatch(string: string, regex: string): string ``` #### Returns Returns the first string that matches the provided regex.