Daily discussion -- null, undefined, string (JS)

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< Title > Null, undefined, memory occupation of strings </ Title >
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< Strong > Summary: </ Strong >
// Another note is that although null is an object type, It is very special and stored in the stack itself. You can understand it as a special form of object.
// In other object-oriented languages, strings are stored in the heap, but in JS, the strings are stored in the stack.
// After that, I suddenly thought of the difference between a question and a definition. I thought of it as a thing. Now, when I suddenly want to declare a variable,
// Whether it is in the stack is both memory usage (of course, allCodeCode segments exist, but memory is used, but I am not talking about this). I mean whether undefined variables exist in the stack.
// After thinking for a while, I think it exists because the undefined type has only one undefined value. When the declared variable is not initialized, the default value is the undefined literal.
// Let's Talk About null. In fact, it should have existed in the heap, but the ecmascript implementation in the JS heap is wrong. Now it is also accepted as a placeholder for an object.
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< Script Language = "JavaScript" Type = "Text/JavaScript" >
Alert (Nan = NAN ); // False
Alert (undefined === Undefined ); // True
Alert (undefined =   Null ); // True, because undefined is derived from null.
Alert ( Typeof   Null );
Alert (undefined ===   Null ); // False

// Using the example above, you can write a function to determine whether it is undefined:
VaR Isundefined =   Function (PARAM ){
Return Param === Undefined;
};
// Note that although null is an object type, It is very special and stored in the stack. You can understand it as a special form of object.
// In other object-oriented languages, strings are stored in the heap, but in JS, strings are stored in the stack.
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