--- title: Most JavaScript Developers Get == Wrong in Interviews... description: JavaScript's loose equality operator `==` follows deterministic type coercion rules from the ECMAScript spec, not random behavior. Three core rules govern all... canonical: https://daily.dev/posts/most-javascript-developers-get-wrong-in-interviews-not-because-it-s-hard--i6iheuzwh twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Most JavaScript Developers Get == Wrong in Interviews (Not Because It's Hard) | daily.dev og:description: JavaScript's loose equality operator `==` follows deterministic type coercion rules from the ECMAScript spec, not random behavior. Three core rules govern all... og:url: https://daily.dev/posts/most-javascript-developers-get-wrong-in-interviews-not-because-it-s-hard--i6iheuzwh og:image: https://api.daily.dev/og/posts/I6IheuZwH.png og:image:alt: Most JavaScript Developers Get == Wrong in Interviews (Not Because It's Hard) og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Most JavaScript Developers Get == Wrong in Interviews (Not Because It's Hard) **[Medium](https://daily.dev/sources/medium_js)** · 5 min read · 1 upvotes · 0 comments ## Summary JavaScript's loose equality operator `==` follows deterministic type coercion rules from the ECMAScript spec, not random behavior. Three core rules govern all comparisons: Booleans convert to Numbers, Strings convert to Numbers when compared with Numbers, and Objects convert to primitives via Symbol.toPrimitive → valueOf() → toString(). Applying these rules step-by-step explains classic interview puzzles like `[] == false`, `[null] == 0`, and `[] == ![]` without memorization. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why does [] == false evaluate to true in JavaScript? False converts to the number 0 under the Boolean-to-Number rule. The empty array then converts to a primitive via toString(), producing an empty string, which converts to 0 under the String-to-Number rule. The comparison becomes 0 == 0, which is true. _Developers debugging loose equality quirks like this one can dig deeper into JavaScript coercion rules on daily.dev._ ### Why does [null] == 0 return true in JavaScript? Converting the array [null] to a string via toString() produces an empty string, because null and undefined are rendered as empty strings when arrays are joined. That empty string then converts to the number 0 under the String-to-Number rule, making the comparison 0 == 0, which evaluates to true. _Anyone puzzling over odd array equality results can explore more JavaScript coercion edge cases on daily.dev._ ### What is the object-to-primitive conversion order JavaScript uses for == comparisons? JavaScript first tries Symbol.toPrimitive, then falls back to valueOf(), and finally to toString(). Arrays typically end up using toString(), which is why array-to-primitive comparisons like [] == false or [null] == 0 often resolve through string conversion rather than valueOf(). _Developers working through JavaScript's coercion internals can find more breakdowns like this on daily.dev._ ## Similar posts on daily.dev - [JavaScript Interview Preparation Challenge : Day 2](https://daily.dev/posts/javascript-interview-preparation-challenge-day-2-y9pndxttk) · Medium · 1 upvotes · 0 comments --- Tags: [#javascript](https://daily.dev/tags/javascript), [#interview-questions](https://daily.dev/tags/interview-questions) [View this post on daily.dev](https://daily.dev/posts/most-javascript-developers-get-wrong-in-interviews-not-because-it-s-hard--i6iheuzwh) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Most JavaScript Developers Get == Wrong in Interviews (Not Because It's Hard)","url":"https://daily.dev/posts/most-javascript-developers-get-wrong-in-interviews-not-because-it-s-hard--i6iheuzwh","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/most-javascript-developers-get-wrong-in-interviews-not-because-it-s-hard--i6iheuzwh"},"datePublished":"2026-07-22T06:07:49.695Z","dateModified":"2026-09-14T07:38:27.717Z","description":"JavaScript's loose equality operator `==` follows deterministic type coercion rules from the ECMAScript spec, not random behavior. 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