undefined
undefined is a JavaScript property in the Global category. The undefined primitive value. The syntax is undefined. A typical example: typeof undefined // "undefined". A close sibling is setTimeout(), which executes a function after a delay (ms). A close sibling is clearTimeout(), which cancels a timeout. A close sibling is setInterval(), which repeatedly executes a function with a fixed delay. A close sibling is clearInterval(), which cancels an interval. More about this category: Global functions — setTimeout, fetch, parseInt, and more. Related Global methods: setTimeout(), clearTimeout(), setInterval(), clearInterval(), setImmediate(), queueMicrotask(), fetch(), eval(). This page is part of the free JS Reference documentation covering 1027+ methods, each with syntax, parameters, return values, examples, and common pitfalls. You can try undefined immediately in the JavaScript playground, look up unfamiliar terms in the glossary, or return to the JS Reference homepage.