你即將離開本站

並前往https://interactive-examples.mdn.mozilla.net/pages/js/globalprops-undefined.html

JavaScript Demo: Standard built-in objects - undefined - Mozilla

function test(t) {. if (t === undefined) {. return 'Undefined value!';. } return t;. } let x;. console.log(test(x));. // Expected output: "Undefined value!".

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