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'use strict';
let call = module.exports = {
safe: safeCall,
once: callOnce,
};
/**
* Calls a function with the given arguments, and ensures that the error-first callback is _always_
* invoked exactly once, even if the function throws an error.
*
* @param {function} fn - The function to invoke
* @param {...*} args - The arguments to pass to the function. The final argument must be a callback function.
*/
function safeCall (fn, args) {
// Get the function arguments as an array
args = Array.prototype.slice.call(arguments, 1);
// Replace the callback function with a wrapper that ensures it will only be called once
let callback = call.once(args.pop());
args.push(callback);
try {
fn.apply(null, args);
}
catch (err) {
callback(err);
}
}
/**
* Returns a wrapper function that ensures the given callback function is only called once.
* Subsequent calls are ignored, unless the first argument is an Error, in which case the
* error is thrown.
*
* @param {function} fn - The function that should only be called once
* @returns {function}
*/
function callOnce (fn) {
let fulfilled = false;
return function onceWrapper (err) {
if (!fulfilled) {
fulfilled = true;
return fn.apply(this, arguments);
}
else if (err) {
// The callback has already been called, but now an error has occurred
// (most likely inside the callback function). So re-throw the error,
// so it gets handled further up the call stack
throw err;
}
};
}
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