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

TypeError: Invalid operand to 'in' (Edge)
TypeError: right-hand side of 'in' should be an object, got 'x' (Firefox)
TypeError: cannot use 'in' operator to search for 'x' in 'y' (Firefox, Chrome)

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

"Hello World".indexOf("Hello") !== -1;
// true

var 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)

var foo = { baz: "bar" };
"bar" in foo; // false
"PI" in Math; // true
"pi" in Math; // false

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