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