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- "use strict";
-
- var isPrototype = require("../prototype/is");
-
- // In theory we could rely on Symbol.toStringTag directly,
- // still early native implementation (e.g. in FF) predated symbols
- var objectToString = Object.prototype.toString
- , objectTaggedString = objectToString.call(Promise.resolve());
-
- module.exports = function (value) {
- if (!value) return false;
-
- // Sanity check (reject objects which do not expose common Promise interface)
- try {
- if (typeof value.then !== "function") return false;
- if (typeof value["catch"] !== "function") return false;
- } catch (error) {
- return false;
- }
-
- // Ensure its native Promise object (has [[PromiseState]] slot)
- // Note: it's not 100% precise as string tag may be overriden
- // and other objects could be hacked to expose it
- if (objectToString.call(value) !== objectTaggedString) return false;
-
- return !isPrototype(value);
- };
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