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metamask-extension/app/scripts/lib/nodeify.js

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import promiseToCallback from 'promise-to-callback';
const callbackNoop = function (err) {
if (err) {
throw err;
}
};
/**
* A generator that returns a function which, when passed a promise, can treat that promise as a node style callback.
* The prime advantage being that callbacks are better for error handling.
*
* @param {Function} fn - The function to handle as a callback
* @param {Object} context - The context in which the fn is to be called, most often a this reference
*
*/
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export default function nodeify(fn, context) {
return function (...args) {
const lastArg = args[args.length - 1];
const lastArgIsCallback = typeof lastArg === 'function';
let callback;
if (lastArgIsCallback) {
callback = lastArg;
args.pop();
} else {
callback = callbackNoop;
}
// call the provided function and ensure result is a promise
let result;
try {
result = Promise.resolve(fn.apply(context, args));
} catch (err) {
result = Promise.reject(err);
}
// wire up promise resolution to callback
promiseToCallback(result)(callback);
};
}