73 lines
2.5 KiB
JavaScript
Executable file
73 lines
2.5 KiB
JavaScript
Executable file
/**
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* This file implements jasminewd's peculiar alternatives to Promise.resolve()
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* and Promise.all(). Do not use the code from this file as polyfill for
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* Promise.resolve() or Promise.all(). There are a number of reasons why this
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* implementation will cause unexpected errors in most codebases.
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*
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* Called "maybePromise" because both the parameters and the return values may
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* or may not be promises, and code execution may or may not be synchronous.
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*/
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/**
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* Determines if a value is a promise.
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*
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* @param {*} val The value to check.
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* @return {boolean} true if val is a promise, false otherwise.
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*/
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function isPromise(val) {
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return val && (typeof val.then == 'function');
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}
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/**
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* Runs a callback synchronously against non-promise values and asynchronously
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* against promises. Similar to ES6's `Promise.resolve` except that it is
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* synchronous when possible and won't wrap the return value.
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*
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* This is not what you normally want. Normally you want the code to be
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* consistently asynchronous, and you want the result wrapped into a promise.
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* But because of webdriver's control flow, we're better off not introducing any
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* extra layers of promises or asynchronous activity.
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*
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* @param {*} val The value to call the callback with.
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* @param {!Function} callback The callback function
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* @return {*} If val isn't a promise, the return value of the callback is
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* directly returned. If val is a promise, a promise (generated by val.then)
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* resolving to the callback's return value is returned.
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*/
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var maybePromise = module.exports = function maybePromise(val, callback) {
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if (isPromise(val)) {
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return val.then(callback);
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} else {
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return callback(val);
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}
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}
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maybePromise.isPromise = isPromise;
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/**
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* Like maybePromise() but for an array of values. Analogous to `Promise.all`.
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*
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* @param {!Array<*>} vals An array of values to call the callback with
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* @param {!Function} callback the callback function
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* @return {*} If nothing in vals is a promise, the return value of the callback
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* is directly returned. Otherwise, a promise (generated by the .then
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* functions in vals) resolving to the callback's return value is returned.
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*/
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maybePromise.all = function all(vals, callback) {
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var resolved = new Array(vals.length);
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function resolveAt(i) {
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if (i >= vals.length) {
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return callback(resolved);
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} else {
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return maybePromise(vals[i], function(val) {
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resolved[i] = val;
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return resolveAt(i+1);
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});
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}
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}
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return resolveAt(0);
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}
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