What is || operator in javascript [duplicate] - javascript

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Logical operator || in javascript, 0 stands for Boolean false?
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What does "var FOO = FOO || {}" (assign a variable or an empty object to that variable) mean in Javascript?
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Closed 5 years ago.
let x = process.argv[2] || "abc";
I am new to javascript.
I don't think || is a boolean OR operator here.
What does this line mean? Why using OR on some strings?
Does this mean if process.argv[2] is null, then assign "abc" to x?

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In auditing the Javascript version of 'verb', (a NURB library,) I happened across this method:
HxOverrides.cca = function(s,index) {
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I'm puzzled by the condition,
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When is this ever True?

In further reading, I discovered the Javascript method, "s.charCodeAt(index)" returns the Unicode value of the (index)th character in string 's'. Specifically:
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In the console, I tested:
NaN == NaN
I found this to be false. Therefore, as to the question of:
"When does x not equal x?"
the answer (at least in Javascript,) is:
"x != x when x is NaN (not a number)".

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JavaScript equivalent of ?? operator in C# [duplicate]

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Is there a "null coalescing" operator in JavaScript?
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Closed 7 years ago.
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var count = something ?? 0;

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Difference between != null and !== null in Javascript [duplicate]

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Splitting hair here, but my editor complains I should use a !== null instead of a != null in a Javascript if statement. What is the difference?
Update
This question has been closed as duplicate, but the other questions supposedly answering my question are not answering it... Check their answers! There is a subtlety here -> null

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