indexOf ( 'nice', 3 ) != - 1 //false 'a nice string'. indexOf ( 'nice' ) != - 1 //true 'a nice string'. The Array.includes method is not declared as a type guard like this, and should not be: if a type guard returns false that should mean the argument is not of the type it guards, but generally if an array of some type T does not include an element, that does not mean the element is not of type T. The includes method will return true if the value is contained in the array and false otherwise. Like includes(), the second parameters sets the starting point: 'a nice string'. Check if an Object is contained in an Array in TypeScript Check if an Array contains a Value in TypeScript Use the includes () method to check if an array contains a value in TypeScript.
If the substring is found, it returns the index of the character that starts the string.
Pre-ES6, the common way to check if a string contains a substring was to use indexOf, which is a string method that return -1 if the string does not contain the substring. includes ( 'nice', 2 ) //true Pre-ES6 alternative to includes(): indexOf() includes ( 'nice', 3 ) //false 'a nice string'. includes () to see if an array includes an item unless your array has more than 100,000 items. 1 Answer Sorted by: 1 You can make use of a user-defined type guard which is a function where you assert 'if this function returns true, then some variable is some type.' We can use includes as the implementation of the function and assert your type through the return. includes ( 'nice' ) //true 'a nice string'. Includes() also accepts an optional second parameter, an integer which indicates the position where to start searching for: 'a nice string'. To use it on all browsers, use Polyfill.io or another dedicated polyfill. It’s supported in all modern browsers except Internet Explorer: This method was introduced in ES6/ES2015. Try it Syntax includes(searchString) includes(searchString, position) Parameters searchString A string to be searched for within str. The most simple one, and also the canonical one going forward, is using the includes() method on a string: 'a nice string'. The includes () method performs a case-sensitive search to determine whether one string may be found within another string, returning true or false as appropriate. JavaScript offers different ways to perform this operation.
Reporter.JavaScript offers many ways to check if a string contains a substring.
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