Conditional/Ternary operator
Syntax=>  condition ? exprIfTrue : exprIfFalse
Example=> (age>10) "old" ? "young"

If condition is true or truthy, do 1st expression else do 2nd expression

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Falsy: value that is considered false when encountered in a Boolean context
0, null, NaN, undefined, empty string: "  "

Truthy: anything but falsy.
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Logical OR operator
Syntax=> leftExpr || rightExpr
Example=> let name= result || "Unknown";

If result is 0, null, NaN, undefined or an empty string: "  ", let name be "Unknown"
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Nullish coalescing operator
Syntax=> leftExpr ?? rightExpr
Example=> let name= result ?? "Unknown";

If result is null or undefined let name be "Unknown"
Same as logical OR but if first operand is NaN, 0, or an empty string, it uses the value,
rather than taking the value of the 2nd operand


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How to select elements whose IDs contain a dot
Dots are meant for classes so you need to escape them using backslash
Example: <span id="my.span">hi</span>

CSS
#my\.span{
rules
}

JavaScript
document.querySelector("#my\\.span")
Note: 2 backslashes because strings naturally consume backslashes