iife() function in libs/langchain-openai source code.

#openai #javascript #langchain #opensource

In this article, we will review iife() function in libs/langchain-openai source code. We will look at:

What is IIFE?
iife() function in Langchain source code
iife() invocation.

What is IIFE?

An IIFE (Immediately Invoked Function Expression) is an idiom in which a JavaScript function runs as soon as it is defined. It is also known as a self-executing anonymous function. The name IIFE is promoted by Ben Alman in his blog

// standard IIFE
(function () {
  // statements…
})();

// arrow function variant
(() => {
  // statements…
})();

// async IIFE
(async () => {
  // statements…
})();

It contains two major parts:

A function expression. This usually needs to be enclosed in parentheses in order to be parsed correctly.
Immediately calling the function expression. Arguments may be provided, though IIFEs without arguments are more common.

Learn more about IIFE.

iife() function in Langchain source code

At line 11 in langchain-openai/src/utils/headers.ts

you will find this below code

const iife = <T>(fn: () => T) => fn();

This IIFE function is just calling function that is passed as a parameter to this function.

iife() invocation

At line 25 in header.ts, you will find this below code:

const output = iife(() => {
    // If headers is a Headers instance
    if (isHeaders(headers)) {
      return headers;
    }
    // If headers is an array of [key, value] pairs
    else if (Array.isArray(headers)) {
      return new Headers(headers);
    }
    // If headers is a NullableHeaders-like object (has 'values' property that is a Headers)
    else if (
      typeof headers === "object" &&
      headers !== null &&
      "values" in headers &&
      isHeaders(headers.values)
    ) {
      return headers.values;
    }
    // If headers is a plain object
    else if (typeof headers === "object" && headers !== null) {
      const entries: [string, string][] = Object.entries(headers)
        .filter(([, v]) => typeof v === "string")
        .map(([k, v]) => [k, v as string]);
      return new Headers(entries);
    }
    return new Headers();
  });