How do I check whether an array contains a string in TypeScript?

Currently I am using Angular 2.0. I have an array as follows:

var channelArray: Array<string> = ['one', 'two', 'three'];

How can I check in TypeScript whether the channelArray contains a string 'three'?

Solution 1:

The same as in JavaScript, using Array.prototype.indexOf():

console.log(channelArray.indexOf('three') > -1);

Or using ECMAScript 2016 Array.prototype.includes():

console.log(channelArray.includes('three'));

Note that you could also use methods like showed by @Nitzan to find a string. However you wouldn't usually do that for a string array, but rather for an array of objects. There those methods were more sensible. For example

const arr = [{foo: 'bar'}, {foo: 'bar'}, {foo: 'baz'}];
console.log(arr.find(e => e.foo === 'bar')); // {foo: 'bar'} (first match)
console.log(arr.some(e => e.foo === 'bar')); // true
console.log(arr.filter(e => e.foo === 'bar')); // [{foo: 'bar'}, {foo: 'bar'}]

Reference

Array.find()

Array.some()

Array.filter()

Solution 2:

You can use the some method:

console.log(channelArray.some(x => x === "three")); // true

You can use the find method:

console.log(channelArray.find(x => x === "three")); // three

Or you can use the indexOf method:

console.log(channelArray.indexOf("three")); // 2

Solution 3:

If your code is ES7 based (or upper versions):

channelArray.includes('three'); //will return true or false

If not, for example you are using IE with no babel transpile:

channelArray.indexOf('three') !== -1; //will return true or false

the indexOf method will return the position the element has into the array, because of that we use !== different from -1 if the needle is found at the first position.

Solution 4:

Also note that "in" keyword does not work on arrays. It works on objects only.

propName in myObject

Array inclusion test is

myArray.includes('three');

Solution 5:

Use JavaScript Array includes() Method

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var n = fruits.includes("Mango");

Try it Yourself » link

Definition

The includes() method determines whether an array contains a specified element.

This method returns true if the array contains the element, and false if not.