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

To use the _.once() function from the Underscore library in TypeScript, follow these steps:

1. Install Underscore.js library using your preferred package manager. For example, using npm:

   index.ts
   npm install underscore
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2. Import the once function from the Underscore module like this:

   index.ts
   import * as _ from 'underscore';
   const doSomethingOnce = _.once(function() {
       console.log('This will only be logged once!');
   });
   doSomethingOnce(); // This will log 'This will only be logged once!'
   doSomethingOnce(); // This won't log anything
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3. Now you can use the _.once() function to create a new function that can only be executed once. The first time the function is called, it will execute normally, but all subsequent calls will return the result of the first call.

Here's an example of how to use the _.once() function in TypeScript:

index.ts
import * as _ from 'underscore';

function heavyCalculation(): number {
    // Perform some calculations that take a lot of time...
    return 42;
}

const cachedValue = _.once(heavyCalculation);
console.log(cachedValue()); // This will log 42
console.log(cachedValue()); // This won't call the heavyCalculation function again, it will return the cached value (42)
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In this example, the heavyCalculation function is only called once, but its result is cached and returned every time cachedValue is called afterwards. This can be useful when dealing with expensive or time-consuming operations that only need to be performed once.