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