Author: John Au-Yeung

Sometimes, we want to test for array of string type in TypeScript.

In this article, we’ll look at how to test for array of string type in TypeScript.

How to test for array of string type in TypeScript?

To test for array of string type in TypeScript, we can use the Array.isArray and the array every instance method.

For instance, we write

const isArrayOfStrings = (value: any): boolean => {
  return (
    Array.isArray(value) && value.every((item) => typeof item === "string")
  );
};

to call Array.isArray to check if value is an array.

And we use

value.every((item) => typeof item === "string");

to check if every item in value is a string with value.every.

Conclusion

To test for array of string type in TypeScript, we can use the Array.isArray and the array every instance method.

Sometimes, we want to use Object.values with TypeScript.

In this article, we’ll look at how to use Object.values with TypeScript.

How to use Object.values with TypeScript?

To use Object.values with TypeScript, we should set the compilerOptions.lib option to include 'es2017' or a later version of JavaScript.

For instance, we write

{
  //...
  "compilerOptions": {
    "lib": ["es2017", "dom"]
  }
  //...
}

in tsconfig.json to include 'es2017' in the compilerOptions.lib array so that the TypeScript compiler is aware that features in ES2017, including Object.values are available.

Conclusion

To use Object.values with TypeScript, we should set the compilerOptions.lib option to include 'es2017' or a later version of JavaScript.

Sometimes, we want to configure custom global interfaces (.d.ts files) for TypeScript.

In this article, we’ll look at how to configure custom global interfaces (.d.ts files) for TypeScript.

How to configure custom global interfaces (.d.ts files) for TypeScript?

To configure custom global interfaces (.d.ts files) for TypeScript, we add our interfaces directly into a .d.ts file.

For instance, we can add a types.d.ts file and write

interface Dictionary {}
interface Foo {}
interface Bar {}

to add the Dictionary, Foo, and Bar interfaces into the types.d.ts global type definition file.

Conclusion

To configure custom global interfaces (.d.ts files) for TypeScript, we add our interfaces directly into a .d.ts file.

Sometimes, we want to declare an array in TypeScript.

In this article, we’ll look at how to declare an array in TypeScript.

How to declare an array in TypeScript?

To declare an array in TypeScript, we can declare them in several different ways.

For instance, we write

const arr1: boolean[] = [];
const arr2: Array<boolean> = [];
const arr3 = [] as boolean[];
const arr4 = <boolean[]>[];
const arr5 = <Array<boolean>>new Array();

to declare a boolean array in 5 different ways.

We can set the variable type to boolean[] or Array<boolean>.

And we can cast the type of the variable to a boolean array with as boolean[], <boolean[]>, or <Array<boolean>>.

Conclusion

To declare an array in TypeScript, we can declare them in several different ways.

Sometimes, we want to create enum like type in TypeScript.

In this article, we’ll look at how to create enum like type in TypeScript.

How to create enum like type in TypeScript?

To create enum like type in TypeScript, we can use the enum keyword.

For instance, we write

enum Fruit {
  APPLE,
  ORANGE,
}

to create the Fruit enum with the APPLE and ORANGE values.

Conclusion

To create enum like type in TypeScript, we can use the enum keyword.