I find it quite surprising that the code below, when entered into the Chrome JavaScript console:
{} instanceof Object
leads to the error message displayed below:
Uncaught SyntaxError: Unexpected token instanceof
Could someone kindly explain why this occurs and provide a solution?
The syntax rule for the instanceof operator is as follows:
RelationalExpression instanceof ShiftExpression
according to ECMA-262 §11.8.
When a statement begins with the punctuator {, it signifies the start of a block, and the closing } marks the end of the statement.
However, if the instanceof operator comes right after the opening brace, it causes confusion because it must follow a RelationalExpression.
To avoid this issue, you can make sure the parser interprets {} as an object literal by adding something before it in the statement, like so:
({}) instanceof Object
{} is considered a block rather than an object literal in that specific scenario.
To convert it into an object literal, you must adjust the context by enclosing it within parentheses like this: ({}).
({}) instanceof Object;
When attempting the following:
var a = {}
a instanceof Object
The result is true, as expected.
However, in your specific scenario
{} instanceof Object
This does not yield true.
The latter is distinct from the former. The initial case involves creating an object literal, whereas the second case does not. This discrepancy leads to the issue you are experiencing.
Give it a go
let x = {}
x instanceof Object
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