how to use the isnull function from the underscore library in typescript

You can use the isnull function from the underscore library in typescript by importing the library and the types. First, install the library:

npm install underscore
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Then, install the type definitions:

npm install --save-dev @types/underscore
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After the installation, import the library and the types:

index.ts
import * as _ from 'underscore';
import { isNull } from 'underscore';

// Example usage
const str = null;
console.log(_.isNull(str)); // true
console.log(isNull(str)); // true
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In the example above, we import the entire underscore library as _, and then we import only the isNull function. Then, we use the function to check if a variable str is null.

Note that the isNull function is just an alias for the === null comparison operator. If you need to check for null and undefined values, you can use the isUndefined function or the _.isUndefined method from underscore.

index.ts
import * as _ from 'underscore';
import { isUndefined } from 'underscore';

// Example usage
let str: string;
console.log(_.isUndefined(str)); // true
console.log(isUndefined(str)); // true
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