[javascript] 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'?

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

TS has many utility methods for arrays which are available via the prototype of Arrays. There are multiple which can achieve this goal but the two most convenient for this purpose are:

1. Array.indexOf() Takes any value as an argument and then returns the first index at which a given element can be found in the array, or -1 if it is not present.
2. Array.includes() Takes any value as an argument and then determines whether an array includes a this value. The method returning true if the value is found, otherwise false.

Example:

const channelArray: string[] = ['one', 'two', 'three'];

console.log(channelArray.indexOf('three'));      // 2
console.log(channelArray.indexOf('three') > -1); // true
console.log(channelArray.indexOf('four') > -1);  // false
console.log(channelArray.includes('three'));     // true

do like this:

departments: string[]=[];
if(this.departments.indexOf(this.departmentName.trim()) >-1 ){
            return;
    }

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');

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.

You can use filter too

this.products = array_products.filter((x) => x.Name.includes("ABC"))

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.