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TypeError: cannot use 'in' operator to search for 'x' in 'y'

JavaScript "right-hand side of 'in' should be an object" in 

TypeError: Cannot use 'in' operator to search for 'x' in 'y' (V8-based & Firefox)
TypeError: right-hand side of 'in' should be an object, got null (Firefox)
TypeError: "y" is not an Object. (evaluating '"x" in "y"') (Safari)

TypeError

in

(Python ) in

js
"Hello" in "Hello World";
// TypeError: cannot use 'in' operator to search for 'Hello' in 'Hello World'

String.prototype.includes()

js
"Hello World".includes("Hello");
// true

null undefined

null undefined

js
const foo = null;
"bar" in foo;
// TypeError: cannot use 'in' operator to search for 'bar' in 'foo' (Chrome)
// TypeError: right-hand side of 'in' should be an object, got null (Firefox)

in

js
const foo = { baz: "bar" };
"bar" in foo; // false

"PI" in Math; // true
"pi" in Math; // false

in Array in

js
const trees = ["redwood", "bay", "cedar", "oak", "maple"];
3 in trees; // true
"oak" in trees; // false

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    43. SyntaxError: incomplete quantifier in regular expression
    44. SyntaxError: invalid assignment left-hand side
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    46. SyntaxError: invalid capture group name in regular expression
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    48. SyntaxError: invalid class set operation in regular expression
    49. SyntaxError: invalid decimal escape in regular expression
    50. SyntaxError: invalid identity escape in regular expression
    51. SyntaxError: invalid named capture reference in regular expression
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    53. SyntaxError: invalid range in character class
    54. SyntaxError: invalid regexp group
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    60. SyntaxError: missing ) after argument list
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    108. TypeError: can't redefine non-configurable property "x"
    109. TypeError: can't set prototype of this object
    110. TypeError: can't set prototype: it would cause a prototype chain cycle
    111. TypeError: cannot use 'in' operator to search for 'x' in 'y'
    112. TypeError: class constructors must be invoked with 'new'
    113. TypeError: cyclic object value
    114. TypeError: derived class constructor returned invalid value x
    115. TypeError: getting private setter-only property
    116. TypeError: Initializing an object twice is an error with private fields/methods
    117. TypeError: invalid 'instanceof' operand 'x'
    118. TypeError: invalid Array.prototype.sort argument
    119. TypeError: invalid assignment to const "x"
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