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In JavaScript, undefined is a special value. It means a variable has been declared, but no value has been assigned yet. not defined , on the other hand, means the engine can't find a reference to that name in memory at all.
Destructuring is a way to extract values from arrays and objects.
Most developers learn JS by trial and error. We see "weird" behaviors—like hoisting or this binding—and just find workarounds.
| Concept | Weird Behavior | |---------|----------------| | NaN === NaN | false | | typeof null | "object" | | [] + [] | "" (empty string) | | [] + {} | "[object Object]" | | {} + [] | 0 | | +!![] | 1 | | 0.1 + 0.2 | 0.30000000000000004 |
"Hey, Web API!" V8 shouted. "I can't handle this right now. You deal with it. Tell me when it's ready!"
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In JavaScript, undefined is a special value. It means a variable has been declared, but no value has been assigned yet. not defined , on the other hand, means the engine can't find a reference to that name in memory at all. js understanding the weird parts
Destructuring is a way to extract values from arrays and objects. ; In JavaScript, undefined is a special value
Most developers learn JS by trial and error. We see "weird" behaviors—like hoisting or this binding—and just find workarounds. Destructuring is a way to extract values from
| Concept | Weird Behavior | |---------|----------------| | NaN === NaN | false | | typeof null | "object" | | [] + [] | "" (empty string) | | [] + {} | "[object Object]" | | {} + [] | 0 | | +!![] | 1 | | 0.1 + 0.2 | 0.30000000000000004 |
"Hey, Web API!" V8 shouted. "I can't handle this right now. You deal with it. Tell me when it's ready!"